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<div class="section" id="module-re">
<span id="re-regular-expression-operations"></span><h1>7.2. <a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> — Regular expression operations<a class="headerlink" href="#module-re" title="Permalink to this headline">¶</a></h1>
<p>This module provides regular expression matching operations similar to
those found in Perl. Both patterns and strings to be searched can be
Unicode strings as well as 8-bit strings.</p>
<p>Regular expressions use the backslash character (<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) to indicate
special forms or to allow special characters to be used without invoking
their special meaning. This collides with Python’s usage of the same
character for the same purpose in string literals; for example, to match
a literal backslash, one might have to write <code class="docutils literal notranslate"><span class="pre">'\\\\'</span></code> as the pattern
string, because the regular expression must be <code class="docutils literal notranslate"><span class="pre">\\</span></code>, and each
backslash must be expressed as <code class="docutils literal notranslate"><span class="pre">\\</span></code> inside a regular Python string
literal.</p>
<p>The solution is to use Python’s raw string notation for regular expression
patterns; backslashes are not handled in any special way in a string literal
prefixed with <code class="docutils literal notranslate"><span class="pre">'r'</span></code>. So <code class="docutils literal notranslate"><span class="pre">r"\n"</span></code> is a two-character string containing
<code class="docutils literal notranslate"><span class="pre">'\'</span></code> and <code class="docutils literal notranslate"><span class="pre">'n'</span></code>, while <code class="docutils literal notranslate"><span class="pre">"\n"</span></code> is a one-character string containing a
newline. Usually patterns will be expressed in Python code using this raw
string notation.</p>
<p>It is important to note that most regular expression operations are available as
module-level functions and <a class="reference internal" href="#re.RegexObject" title="re.RegexObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">RegexObject</span></code></a> methods. The functions are
shortcuts that don’t require you to compile a regex object first, but miss some
fine-tuning parameters.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The third-party <a class="reference external" href="https://pypi.org/project/regex/">regex</a> module,
which has an API compatible with the standard library <a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> module,
but offers additional functionality and a more thorough Unicode support.</p>
</div>
<div class="section" id="regular-expression-syntax">
<span id="re-syntax"></span><h2>7.2.1. Regular Expression Syntax<a class="headerlink" href="#regular-expression-syntax" title="Permalink to this headline">¶</a></h2>
<p>A regular expression (or RE) specifies a set of strings that matches it; the
functions in this module let you check if a particular string matches a given
regular expression (or if a given regular expression matches a particular
string, which comes down to the same thing).</p>
<p>Regular expressions can be concatenated to form new regular expressions; if <em>A</em>
and <em>B</em> are both regular expressions, then <em>AB</em> is also a regular expression.
In general, if a string <em>p</em> matches <em>A</em> and another string <em>q</em> matches <em>B</em>, the
string <em>pq</em> will match AB. This holds unless <em>A</em> or <em>B</em> contain low precedence
operations; boundary conditions between <em>A</em> and <em>B</em>; or have numbered group
references. Thus, complex expressions can easily be constructed from simpler
primitive expressions like the ones described here. For details of the theory
and implementation of regular expressions, consult the Friedl book referenced
above, or almost any textbook about compiler construction.</p>
<p>A brief explanation of the format of regular expressions follows. For further
information and a gentler presentation, consult the <a class="reference internal" href="../howto/regex.html#regex-howto"><span class="std std-ref">Regular Expression HOWTO</span></a>.</p>
<p>Regular expressions can contain both special and ordinary characters. Most
ordinary characters, like <code class="docutils literal notranslate"><span class="pre">'A'</span></code>, <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'0'</span></code>, are the simplest regular
expressions; they simply match themselves. You can concatenate ordinary
characters, so <code class="docutils literal notranslate"><span class="pre">last</span></code> matches the string <code class="docutils literal notranslate"><span class="pre">'last'</span></code>. (In the rest of this
section, we’ll write RE’s in <code class="docutils literal notranslate"><span class="pre">this</span> <span class="pre">special</span> <span class="pre">style</span></code>, usually without quotes, and
strings to be matched <code class="docutils literal notranslate"><span class="pre">'in</span> <span class="pre">single</span> <span class="pre">quotes'</span></code>.)</p>
<p>Some characters, like <code class="docutils literal notranslate"><span class="pre">'|'</span></code> or <code class="docutils literal notranslate"><span class="pre">'('</span></code>, are special. Special
characters either stand for classes of ordinary characters, or affect
how the regular expressions around them are interpreted. Regular
expression pattern strings may not contain null bytes, but can specify
the null byte using the <code class="docutils literal notranslate"><span class="pre">\number</span></code> notation, e.g., <code class="docutils literal notranslate"><span class="pre">'\x00'</span></code>.</p>
<p>Repetition qualifiers (<code class="docutils literal notranslate"><span class="pre">*</span></code>, <code class="docutils literal notranslate"><span class="pre">+</span></code>, <code class="docutils literal notranslate"><span class="pre">?</span></code>, <code class="docutils literal notranslate"><span class="pre">{m,n}</span></code>, etc) cannot be
directly nested. This avoids ambiguity with the non-greedy modifier suffix
<code class="docutils literal notranslate"><span class="pre">?</span></code>, and with other modifiers in other implementations. To apply a second
repetition to an inner repetition, parentheses may be used. For example,
the expression <code class="docutils literal notranslate"><span class="pre">(?:a{6})*</span></code> matches any multiple of six <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters.</p>
<p>The special characters are:</p>
<dl class="docutils">
<dt><code class="docutils literal notranslate"><span class="pre">'.'</span></code></dt>
<dd>(Dot.) In the default mode, this matches any character except a newline. If
the <a class="reference internal" href="#re.DOTALL" title="re.DOTALL"><code class="xref py py-const docutils literal notranslate"><span class="pre">DOTALL</span></code></a> flag has been specified, this matches any character
including a newline.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'^'</span></code></dt>
<dd>(Caret.) Matches the start of the string, and in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode also
matches immediately after each newline.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'$'</span></code></dt>
<dd>Matches the end of the string or just before the newline at the end of the
string, and in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode also matches before a newline. <code class="docutils literal notranslate"><span class="pre">foo</span></code>
matches both ‘foo’ and ‘foobar’, while the regular expression <code class="docutils literal notranslate"><span class="pre">foo$</span></code> matches
only ‘foo’. More interestingly, searching for <code class="docutils literal notranslate"><span class="pre">foo.$</span></code> in <code class="docutils literal notranslate"><span class="pre">'foo1\nfoo2\n'</span></code>
matches ‘foo2’ normally, but ‘foo1’ in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode; searching for
a single <code class="docutils literal notranslate"><span class="pre">$</span></code> in <code class="docutils literal notranslate"><span class="pre">'foo\n'</span></code> will find two (empty) matches: one just before
the newline, and one at the end of the string.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'*'</span></code></dt>
<dd>Causes the resulting RE to match 0 or more repetitions of the preceding RE, as
many repetitions as are possible. <code class="docutils literal notranslate"><span class="pre">ab*</span></code> will match ‘a’, ‘ab’, or ‘a’ followed
by any number of ‘b’s.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'+'</span></code></dt>
<dd>Causes the resulting RE to match 1 or more repetitions of the preceding RE.
<code class="docutils literal notranslate"><span class="pre">ab+</span></code> will match ‘a’ followed by any non-zero number of ‘b’s; it will not
match just ‘a’.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'?'</span></code></dt>
<dd>Causes the resulting RE to match 0 or 1 repetitions of the preceding RE.
<code class="docutils literal notranslate"><span class="pre">ab?</span></code> will match either ‘a’ or ‘ab’.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">+?</span></code>, <code class="docutils literal notranslate"><span class="pre">??</span></code></dt>
<dd>The <code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>, and <code class="docutils literal notranslate"><span class="pre">'?'</span></code> qualifiers are all <em class="dfn">greedy</em>; they match
as much text as possible. Sometimes this behaviour isn’t desired; if the RE
<code class="docutils literal notranslate"><span class="pre"><.*></span></code> is matched against <code class="docutils literal notranslate"><span class="pre"><a></span> <span class="pre">b</span> <span class="pre"><c></span></code>, it will match the entire
string, and not just <code class="docutils literal notranslate"><span class="pre"><a></span></code>. Adding <code class="docutils literal notranslate"><span class="pre">?</span></code> after the qualifier makes it
perform the match in <em class="dfn">non-greedy</em> or <em class="dfn">minimal</em> fashion; as <em>few</em>
characters as possible will be matched. Using the RE <code class="docutils literal notranslate"><span class="pre"><.*?></span></code> will match
only <code class="docutils literal notranslate"><span class="pre"><a></span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m}</span></code></dt>
<dd>Specifies that exactly <em>m</em> copies of the previous RE should be matched; fewer
matches cause the entire RE not to match. For example, <code class="docutils literal notranslate"><span class="pre">a{6}</span></code> will match
exactly six <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters, but not five.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}</span></code></dt>
<dd>Causes the resulting RE to match from <em>m</em> to <em>n</em> repetitions of the preceding
RE, attempting to match as many repetitions as possible. For example,
<code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> will match from 3 to 5 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters. Omitting <em>m</em> specifies a
lower bound of zero, and omitting <em>n</em> specifies an infinite upper bound. As an
example, <code class="docutils literal notranslate"><span class="pre">a{4,}b</span></code> will match <code class="docutils literal notranslate"><span class="pre">aaaab</span></code> or a thousand <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters
followed by a <code class="docutils literal notranslate"><span class="pre">b</span></code>, but not <code class="docutils literal notranslate"><span class="pre">aaab</span></code>. The comma may not be omitted or the
modifier would be confused with the previously described form.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}?</span></code></dt>
<dd>Causes the resulting RE to match from <em>m</em> to <em>n</em> repetitions of the preceding
RE, attempting to match as <em>few</em> repetitions as possible. This is the
non-greedy version of the previous qualifier. For example, on the
6-character string <code class="docutils literal notranslate"><span class="pre">'aaaaaa'</span></code>, <code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> will match 5 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters,
while <code class="docutils literal notranslate"><span class="pre">a{3,5}?</span></code> will only match 3 characters.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'\'</span></code></dt>
<dd><p class="first">Either escapes special characters (permitting you to match characters like
<code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'?'</span></code>, and so forth), or signals a special sequence; special
sequences are discussed below.</p>
<p class="last">If you’re not using a raw string to express the pattern, remember that Python
also uses the backslash as an escape sequence in string literals; if the escape
sequence isn’t recognized by Python’s parser, the backslash and subsequent
character are included in the resulting string. However, if Python would
recognize the resulting sequence, the backslash should be repeated twice. This
is complicated and hard to understand, so it’s highly recommended that you use
raw strings for all but the simplest expressions.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">[]</span></code></dt>
<dd><p class="first">Used to indicate a set of characters. In a set:</p>
<ul class="last simple">
<li>Characters can be listed individually, e.g. <code class="docutils literal notranslate"><span class="pre">[amk]</span></code> will match <code class="docutils literal notranslate"><span class="pre">'a'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'m'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'k'</span></code>.</li>
<li>Ranges of characters can be indicated by giving two characters and separating
them by a <code class="docutils literal notranslate"><span class="pre">'-'</span></code>, for example <code class="docutils literal notranslate"><span class="pre">[a-z]</span></code> will match any lowercase ASCII letter,
<code class="docutils literal notranslate"><span class="pre">[0-5][0-9]</span></code> will match all the two-digits numbers from <code class="docutils literal notranslate"><span class="pre">00</span></code> to <code class="docutils literal notranslate"><span class="pre">59</span></code>, and
<code class="docutils literal notranslate"><span class="pre">[0-9A-Fa-f]</span></code> will match any hexadecimal digit. If <code class="docutils literal notranslate"><span class="pre">-</span></code> is escaped (e.g.
<code class="docutils literal notranslate"><span class="pre">[a\-z]</span></code>) or if it’s placed as the first or last character (e.g. <code class="docutils literal notranslate"><span class="pre">[a-]</span></code>),
it will match a literal <code class="docutils literal notranslate"><span class="pre">'-'</span></code>.</li>
<li>Special characters lose their special meaning inside sets. For example,
<code class="docutils literal notranslate"><span class="pre">[(+*)]</span></code> will match any of the literal characters <code class="docutils literal notranslate"><span class="pre">'('</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'*'</span></code>, or <code class="docutils literal notranslate"><span class="pre">')'</span></code>.</li>
<li>Character classes such as <code class="docutils literal notranslate"><span class="pre">\w</span></code> or <code class="docutils literal notranslate"><span class="pre">\S</span></code> (defined below) are also accepted
inside a set, although the characters they match depends on whether
<a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> or <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> mode is in force.</li>
<li>Characters that are not within a range can be matched by <em class="dfn">complementing</em>
the set. If the first character of the set is <code class="docutils literal notranslate"><span class="pre">'^'</span></code>, all the characters
that are <em>not</em> in the set will be matched. For example, <code class="docutils literal notranslate"><span class="pre">[^5]</span></code> will match
any character except <code class="docutils literal notranslate"><span class="pre">'5'</span></code>, and <code class="docutils literal notranslate"><span class="pre">[^^]</span></code> will match any character except
<code class="docutils literal notranslate"><span class="pre">'^'</span></code>. <code class="docutils literal notranslate"><span class="pre">^</span></code> has no special meaning if it’s not the first character in
the set.</li>
<li>To match a literal <code class="docutils literal notranslate"><span class="pre">']'</span></code> inside a set, precede it with a backslash, or
place it at the beginning of the set. For example, both <code class="docutils literal notranslate"><span class="pre">[()[\]{}]</span></code> and
<code class="docutils literal notranslate"><span class="pre">[]()[{}]</span></code> will both match a parenthesis.</li>
</ul>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">'|'</span></code></dt>
<dd><code class="docutils literal notranslate"><span class="pre">A|B</span></code>, where A and B can be arbitrary REs, creates a regular expression that
will match either A or B. An arbitrary number of REs can be separated by the
<code class="docutils literal notranslate"><span class="pre">'|'</span></code> in this way. This can be used inside groups (see below) as well. As
the target string is scanned, REs separated by <code class="docutils literal notranslate"><span class="pre">'|'</span></code> are tried from left to
right. When one pattern completely matches, that branch is accepted. This means
that once <code class="docutils literal notranslate"><span class="pre">A</span></code> matches, <code class="docutils literal notranslate"><span class="pre">B</span></code> will not be tested further, even if it would
produce a longer overall match. In other words, the <code class="docutils literal notranslate"><span class="pre">'|'</span></code> operator is never
greedy. To match a literal <code class="docutils literal notranslate"><span class="pre">'|'</span></code>, use <code class="docutils literal notranslate"><span class="pre">\|</span></code>, or enclose it inside a
character class, as in <code class="docutils literal notranslate"><span class="pre">[|]</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(...)</span></code></dt>
<dd>Matches whatever regular expression is inside the parentheses, and indicates the
start and end of a group; the contents of a group can be retrieved after a match
has been performed, and can be matched later in the string with the <code class="docutils literal notranslate"><span class="pre">\number</span></code>
special sequence, described below. To match the literals <code class="docutils literal notranslate"><span class="pre">'('</span></code> or <code class="docutils literal notranslate"><span class="pre">')'</span></code>,
use <code class="docutils literal notranslate"><span class="pre">\(</span></code> or <code class="docutils literal notranslate"><span class="pre">\)</span></code>, or enclose them inside a character class: <code class="docutils literal notranslate"><span class="pre">[(]</span> <span class="pre">[)]</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?...)</span></code></dt>
<dd>This is an extension notation (a <code class="docutils literal notranslate"><span class="pre">'?'</span></code> following a <code class="docutils literal notranslate"><span class="pre">'('</span></code> is not meaningful
otherwise). The first character after the <code class="docutils literal notranslate"><span class="pre">'?'</span></code> determines what the meaning
and further syntax of the construct is. Extensions usually do not create a new
group; <code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code> is the only exception to this rule. Following are the
currently supported extensions.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?iLmsux)</span></code></dt>
<dd><p class="first">(One or more letters from the set <code class="docutils literal notranslate"><span class="pre">'i'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code>, <code class="docutils literal notranslate"><span class="pre">'m'</span></code>, <code class="docutils literal notranslate"><span class="pre">'s'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'u'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code>.) The group matches the empty string; the letters
set the corresponding flags: <a class="reference internal" href="#re.I" title="re.I"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.I</span></code></a> (ignore case),
<a class="reference internal" href="#re.L" title="re.L"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.L</span></code></a> (locale dependent), <a class="reference internal" href="#re.M" title="re.M"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.M</span></code></a> (multi-line),
<a class="reference internal" href="#re.S" title="re.S"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.S</span></code></a> (dot matches all), <a class="reference internal" href="#re.U" title="re.U"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code></a> (Unicode dependent),
and <a class="reference internal" href="#re.X" title="re.X"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.X</span></code></a> (verbose), for the entire regular expression. (The
flags are described in <a class="reference internal" href="#contents-of-module-re"><span class="std std-ref">Module Contents</span></a>.) This
is useful if you wish to include the flags as part of the regular
expression, instead of passing a <em>flag</em> argument to the
<a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> function.</p>
<p class="last">Note that the <code class="docutils literal notranslate"><span class="pre">(?x)</span></code> flag changes how the expression is parsed. It should be
used first in the expression string, or after one or more whitespace characters.
If there are non-whitespace characters before the flag, the results are
undefined.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?:...)</span></code></dt>
<dd>A non-capturing version of regular parentheses. Matches whatever regular
expression is inside the parentheses, but the substring matched by the group
<em>cannot</em> be retrieved after performing a match or referenced later in the
pattern.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code></dt>
<dd><p class="first">Similar to regular parentheses, but the substring matched by the group is
accessible via the symbolic group name <em>name</em>. Group names must be valid
Python identifiers, and each group name must be defined only once within a
regular expression. A symbolic group is also a numbered group, just as if
the group were not named.</p>
<p>Named groups can be referenced in three contexts. If the pattern is
<code class="docutils literal notranslate"><span class="pre">(?P<quote>['"]).*?(?P=quote)</span></code> (i.e. matching a string quoted with either
single or double quotes):</p>
<table border="1" class="last docutils">
<colgroup>
<col width="53%" />
<col width="47%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Context of reference to group “quote”</th>
<th class="head">Ways to reference it</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>in the same pattern itself</td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">(?P=quote)</span></code> (as shown)</li>
<li><code class="docutils literal notranslate"><span class="pre">\1</span></code></li>
</ul>
</td>
</tr>
<tr class="row-odd"><td>when processing match object <code class="docutils literal notranslate"><span class="pre">m</span></code></td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">m.group('quote')</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">m.end('quote')</span></code> (etc.)</li>
</ul>
</td>
</tr>
<tr class="row-even"><td>in a string passed to the <code class="docutils literal notranslate"><span class="pre">repl</span></code>
argument of <code class="docutils literal notranslate"><span class="pre">re.sub()</span></code></td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">\g<quote></span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">\g<1></span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">\1</span></code></li>
</ul>
</td>
</tr>
</tbody>
</table>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?P=name)</span></code></dt>
<dd>A backreference to a named group; it matches whatever text was matched by the
earlier group named <em>name</em>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?#...)</span></code></dt>
<dd>A comment; the contents of the parentheses are simply ignored.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?=...)</span></code></dt>
<dd>Matches if <code class="docutils literal notranslate"><span class="pre">...</span></code> matches next, but doesn’t consume any of the string. This is
called a lookahead assertion. For example, <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?=Asimov)</span></code> will match
<code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> only if it’s followed by <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?!...)</span></code></dt>
<dd>Matches if <code class="docutils literal notranslate"><span class="pre">...</span></code> doesn’t match next. This is a negative lookahead assertion.
For example, <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?!Asimov)</span></code> will match <code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> only if it’s <em>not</em>
followed by <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?<=...)</span></code></dt>
<dd><p class="first">Matches if the current position in the string is preceded by a match for <code class="docutils literal notranslate"><span class="pre">...</span></code>
that ends at the current position. This is called a <em class="dfn">positive lookbehind
assertion</em>. <code class="docutils literal notranslate"><span class="pre">(?<=abc)def</span></code> will find a match in <code class="docutils literal notranslate"><span class="pre">abcdef</span></code>, since the
lookbehind will back up 3 characters and check if the contained pattern matches.
The contained pattern must only match strings of some fixed length, meaning that
<code class="docutils literal notranslate"><span class="pre">abc</span></code> or <code class="docutils literal notranslate"><span class="pre">a|b</span></code> are allowed, but <code class="docutils literal notranslate"><span class="pre">a*</span></code> and <code class="docutils literal notranslate"><span class="pre">a{3,4}</span></code> are not. Group
references are not supported even if they match strings of some fixed length.
Note that
patterns which start with positive lookbehind assertions will not match at the
beginning of the string being searched; you will most likely want to use the
<a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> function rather than the <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> function:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">re</span>
<span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'(?<=abc)def'</span><span class="p">,</span> <span class="s1">'abcdef'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="go">'def'</span>
</pre></div>
</div>
<p>This example looks for a word following a hyphen:</p>
<div class="last highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'(?<=-)\w+'</span><span class="p">,</span> <span class="s1">'spam-egg'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="go">'egg'</span>
</pre></div>
</div>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?<!...)</span></code></dt>
<dd>Matches if the current position in the string is not preceded by a match for
<code class="docutils literal notranslate"><span class="pre">...</span></code>. This is called a <em class="dfn">negative lookbehind assertion</em>. Similar to
positive lookbehind assertions, the contained pattern must only match strings of
some fixed length and shouldn’t contain group references.
Patterns which start with negative lookbehind assertions may
match at the beginning of the string being searched.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?(id/name)yes-pattern|no-pattern)</span></code></dt>
<dd><p class="first">Will try to match with <code class="docutils literal notranslate"><span class="pre">yes-pattern</span></code> if the group with given <em>id</em> or <em>name</em>
exists, and with <code class="docutils literal notranslate"><span class="pre">no-pattern</span></code> if it doesn’t. <code class="docutils literal notranslate"><span class="pre">no-pattern</span></code> is optional and
can be omitted. For example, <code class="docutils literal notranslate"><span class="pre">(<)?(\w+@\w+(?:\.\w+)+)(?(1)>)</span></code> is a poor email
matching pattern, which will match with <code class="docutils literal notranslate"><span class="pre">'<user@host.com>'</span></code> as well as
<code class="docutils literal notranslate"><span class="pre">'user@host.com'</span></code>, but not with <code class="docutils literal notranslate"><span class="pre">'<user@host.com'</span></code>.</p>
<div class="last versionadded">
<p><span class="versionmodified">New in version 2.4.</span></p>
</div>
</dd>
</dl>
<p>The special sequences consist of <code class="docutils literal notranslate"><span class="pre">'\'</span></code> and a character from the list below.
If the ordinary character is not on the list, then the resulting RE will match
the second character. For example, <code class="docutils literal notranslate"><span class="pre">\$</span></code> matches the character <code class="docutils literal notranslate"><span class="pre">'$'</span></code>.</p>
<dl class="docutils">
<dt><code class="docutils literal notranslate"><span class="pre">\number</span></code></dt>
<dd>Matches the contents of the group of the same number. Groups are numbered
starting from 1. For example, <code class="docutils literal notranslate"><span class="pre">(.+)</span> <span class="pre">\1</span></code> matches <code class="docutils literal notranslate"><span class="pre">'the</span> <span class="pre">the'</span></code> or <code class="docutils literal notranslate"><span class="pre">'55</span> <span class="pre">55'</span></code>,
but not <code class="docutils literal notranslate"><span class="pre">'thethe'</span></code> (note the space after the group). This special sequence
can only be used to match one of the first 99 groups. If the first digit of
<em>number</em> is 0, or <em>number</em> is 3 octal digits long, it will not be interpreted as
a group match, but as the character with octal value <em>number</em>. Inside the
<code class="docutils literal notranslate"><span class="pre">'['</span></code> and <code class="docutils literal notranslate"><span class="pre">']'</span></code> of a character class, all numeric escapes are treated as
characters.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\A</span></code></dt>
<dd>Matches only at the start of the string.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\b</span></code></dt>
<dd>Matches the empty string, but only at the beginning or end of a word. A word is
defined as a sequence of alphanumeric or underscore characters, so the end of a
word is indicated by whitespace or a non-alphanumeric, non-underscore character.
Note that formally, <code class="docutils literal notranslate"><span class="pre">\b</span></code> is defined as the boundary between a <code class="docutils literal notranslate"><span class="pre">\w</span></code> and
a <code class="docutils literal notranslate"><span class="pre">\W</span></code> character (or vice versa), or between <code class="docutils literal notranslate"><span class="pre">\w</span></code> and the beginning/end
of the string, so the precise set of characters deemed to be alphanumeric
depends on the values of the <code class="docutils literal notranslate"><span class="pre">UNICODE</span></code> and <code class="docutils literal notranslate"><span class="pre">LOCALE</span></code> flags.
For example, <code class="docutils literal notranslate"><span class="pre">r'\bfoo\b'</span></code> matches <code class="docutils literal notranslate"><span class="pre">'foo'</span></code>, <code class="docutils literal notranslate"><span class="pre">'foo.'</span></code>, <code class="docutils literal notranslate"><span class="pre">'(foo)'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'bar</span> <span class="pre">foo</span> <span class="pre">baz'</span></code> but not <code class="docutils literal notranslate"><span class="pre">'foobar'</span></code> or <code class="docutils literal notranslate"><span class="pre">'foo3'</span></code>.
Inside a character range, <code class="docutils literal notranslate"><span class="pre">\b</span></code> represents the backspace character, for
compatibility with Python’s string literals.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\B</span></code></dt>
<dd>Matches the empty string, but only when it is <em>not</em> at the beginning or end of a
word. This means that <code class="docutils literal notranslate"><span class="pre">r'py\B'</span></code> matches <code class="docutils literal notranslate"><span class="pre">'python'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py3'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py2'</span></code>,
but not <code class="docutils literal notranslate"><span class="pre">'py'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py.'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'py!'</span></code>.
<code class="docutils literal notranslate"><span class="pre">\B</span></code> is just the opposite of <code class="docutils literal notranslate"><span class="pre">\b</span></code>, so is also subject to the settings
of <code class="docutils literal notranslate"><span class="pre">LOCALE</span></code> and <code class="docutils literal notranslate"><span class="pre">UNICODE</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\d</span></code></dt>
<dd>When the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flag is not specified, matches any decimal digit; this
is equivalent to the set <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code>. With <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a>, it will match
whatever is classified as a decimal digit in the Unicode character properties
database.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\D</span></code></dt>
<dd>When the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flag is not specified, matches any non-digit
character; this is equivalent to the set <code class="docutils literal notranslate"><span class="pre">[^0-9]</span></code>. With <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a>, it
will match anything other than character marked as digits in the Unicode
character properties database.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\s</span></code></dt>
<dd>When the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flag is not specified, it matches any whitespace
character, this is equivalent to the set <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code>. The
<a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag has no extra effect on matching of the space.
If <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> is set, this will match the characters <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code>
plus whatever is classified as space in the Unicode character properties
database.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\S</span></code></dt>
<dd>When the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flag is not specified, matches any non-whitespace
character; this is equivalent to the set <code class="docutils literal notranslate"><span class="pre">[^</span> <span class="pre">\t\n\r\f\v]</span></code> The
<a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag has no extra effect on non-whitespace match. If
<a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> is set, then any character not marked as space in the
Unicode character properties database is matched.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\w</span></code></dt>
<dd>When the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> and <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flags are not specified, matches
any alphanumeric character and the underscore; this is equivalent to the set
<code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code>. With <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a>, it will match the set <code class="docutils literal notranslate"><span class="pre">[0-9_]</span></code> plus
whatever characters are defined as alphanumeric for the current locale. If
<a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> is set, this will match the characters <code class="docutils literal notranslate"><span class="pre">[0-9_]</span></code> plus whatever
is classified as alphanumeric in the Unicode character properties database.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\W</span></code></dt>
<dd>When the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> and <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flags are not specified, matches
any non-alphanumeric character; this is equivalent to the set <code class="docutils literal notranslate"><span class="pre">[^a-zA-Z0-9_]</span></code>.
With <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a>, it will match any character not in the set <code class="docutils literal notranslate"><span class="pre">[0-9_]</span></code>, and
not defined as alphanumeric for the current locale. If <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> is set,
this will match anything other than <code class="docutils literal notranslate"><span class="pre">[0-9_]</span></code> plus characters classified as
not alphanumeric in the Unicode character properties database.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\Z</span></code></dt>
<dd>Matches only at the end of the string.</dd>
</dl>
<p>If both <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> and <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flags are included for a
particular sequence, then <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag takes effect first followed by
the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a>.</p>
<p>Most of the standard escapes supported by Python string literals are also
accepted by the regular expression parser:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>\<span class="n">a</span> \<span class="n">b</span> \<span class="n">f</span> \<span class="n">n</span>
\<span class="n">r</span> \<span class="n">t</span> \<span class="n">v</span> \<span class="n">x</span>
\\
</pre></div>
</div>
<p>(Note that <code class="docutils literal notranslate"><span class="pre">\b</span></code> is used to represent word boundaries, and means “backspace”
only inside character classes.)</p>
<p>Octal escapes are included in a limited form: If the first digit is a 0, or if
there are three octal digits, it is considered an octal escape. Otherwise, it is
a group reference. As for string literals, octal escapes are always at most
three digits in length.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>Mastering Regular Expressions</dt>
<dd>Book on regular expressions by Jeffrey Friedl, published by O’Reilly. The
second edition of the book no longer covers Python at all, but the first
edition covered writing good regular expression patterns in great detail.</dd>
</dl>
</div>
</div>
<div class="section" id="module-contents">
<span id="contents-of-module-re"></span><h2>7.2.2. Module Contents<a class="headerlink" href="#module-contents" title="Permalink to this headline">¶</a></h2>
<p>The module defines several functions, constants, and an exception. Some of the
functions are simplified versions of the full featured methods for compiled
regular expressions. Most non-trivial applications always use the compiled
form.</p>
<dl class="function">
<dt id="re.compile">
<code class="descclassname">re.</code><code class="descname">compile</code><span class="sig-paren">(</span><em>pattern</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.compile" title="Permalink to this definition">¶</a></dt>
<dd><p>Compile a regular expression pattern into a regular expression object, which
can be used for matching using its <a class="reference internal" href="#re.RegexObject.match" title="re.RegexObject.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> and
<a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> methods, described below.</p>
<p>The expression’s behaviour can be modified by specifying a <em>flags</em> value.
Values can be any of the following variables, combined using bitwise OR (the
<code class="docutils literal notranslate"><span class="pre">|</span></code> operator).</p>
<p>The sequence</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">prog</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="n">pattern</span><span class="p">)</span>
<span class="n">result</span> <span class="o">=</span> <span class="n">prog</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">string</span><span class="p">)</span>
</pre></div>
</div>
<p>is equivalent to</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">result</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
</pre></div>
</div>
<p>but using <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> and saving the resulting regular expression
object for reuse is more efficient when the expression will be used several
times in a single program.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The compiled versions of the most recent patterns passed to
<a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a>, <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.search()</span></code></a> or <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> are cached, so
programs that use only a few regular expressions at a time needn’t worry
about compiling regular expressions.</p>
</div>
</dd></dl>
<dl class="data">
<dt id="re.DEBUG">
<code class="descclassname">re.</code><code class="descname">DEBUG</code><a class="headerlink" href="#re.DEBUG" title="Permalink to this definition">¶</a></dt>
<dd><p>Display debug information about compiled expression.</p>
</dd></dl>
<dl class="data">
<dt id="re.I">
<code class="descclassname">re.</code><code class="descname">I</code><a class="headerlink" href="#re.I" title="Permalink to this definition">¶</a></dt>
<dt id="re.IGNORECASE">
<code class="descclassname">re.</code><code class="descname">IGNORECASE</code><a class="headerlink" href="#re.IGNORECASE" title="Permalink to this definition">¶</a></dt>
<dd><p>Perform case-insensitive matching; expressions like <code class="docutils literal notranslate"><span class="pre">[A-Z]</span></code> will match
lowercase letters, too. This is not affected by the current locale. To
get this effect on non-ASCII Unicode characters such as <code class="docutils literal notranslate"><span class="pre">ü</span></code> and <code class="docutils literal notranslate"><span class="pre">Ü</span></code>,
add the <a class="reference internal" href="#re.UNICODE" title="re.UNICODE"><code class="xref py py-const docutils literal notranslate"><span class="pre">UNICODE</span></code></a> flag.</p>
</dd></dl>
<dl class="data">
<dt id="re.L">
<code class="descclassname">re.</code><code class="descname">L</code><a class="headerlink" href="#re.L" title="Permalink to this definition">¶</a></dt>
<dt id="re.LOCALE">
<code class="descclassname">re.</code><code class="descname">LOCALE</code><a class="headerlink" href="#re.LOCALE" title="Permalink to this definition">¶</a></dt>
<dd><p>Make <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code>, <code class="docutils literal notranslate"><span class="pre">\s</span></code> and <code class="docutils literal notranslate"><span class="pre">\S</span></code> dependent on the
current locale.</p>
</dd></dl>
<dl class="data">
<dt id="re.M">
<code class="descclassname">re.</code><code class="descname">M</code><a class="headerlink" href="#re.M" title="Permalink to this definition">¶</a></dt>
<dt id="re.MULTILINE">
<code class="descclassname">re.</code><code class="descname">MULTILINE</code><a class="headerlink" href="#re.MULTILINE" title="Permalink to this definition">¶</a></dt>
<dd><p>When specified, the pattern character <code class="docutils literal notranslate"><span class="pre">'^'</span></code> matches at the beginning of the
string and at the beginning of each line (immediately following each newline);
and the pattern character <code class="docutils literal notranslate"><span class="pre">'$'</span></code> matches at the end of the string and at the
end of each line (immediately preceding each newline). By default, <code class="docutils literal notranslate"><span class="pre">'^'</span></code>
matches only at the beginning of the string, and <code class="docutils literal notranslate"><span class="pre">'$'</span></code> only at the end of the
string and immediately before the newline (if any) at the end of the string.</p>
</dd></dl>
<dl class="data">
<dt id="re.S">
<code class="descclassname">re.</code><code class="descname">S</code><a class="headerlink" href="#re.S" title="Permalink to this definition">¶</a></dt>
<dt id="re.DOTALL">
<code class="descclassname">re.</code><code class="descname">DOTALL</code><a class="headerlink" href="#re.DOTALL" title="Permalink to this definition">¶</a></dt>
<dd><p>Make the <code class="docutils literal notranslate"><span class="pre">'.'</span></code> special character match any character at all, including a
newline; without this flag, <code class="docutils literal notranslate"><span class="pre">'.'</span></code> will match anything <em>except</em> a newline.</p>
</dd></dl>
<dl class="data">
<dt id="re.U">
<code class="descclassname">re.</code><code class="descname">U</code><a class="headerlink" href="#re.U" title="Permalink to this definition">¶</a></dt>
<dt id="re.UNICODE">
<code class="descclassname">re.</code><code class="descname">UNICODE</code><a class="headerlink" href="#re.UNICODE" title="Permalink to this definition">¶</a></dt>
<dd><p>Make the <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code>, <code class="docutils literal notranslate"><span class="pre">\d</span></code>, <code class="docutils literal notranslate"><span class="pre">\D</span></code>, <code class="docutils literal notranslate"><span class="pre">\s</span></code> and <code class="docutils literal notranslate"><span class="pre">\S</span></code>
sequences dependent on the Unicode character properties database. Also
enables non-ASCII matching for <a class="reference internal" href="#re.IGNORECASE" title="re.IGNORECASE"><code class="xref py py-const docutils literal notranslate"><span class="pre">IGNORECASE</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.</span></p>
</div>
</dd></dl>
<dl class="data">
<dt id="re.X">
<code class="descclassname">re.</code><code class="descname">X</code><a class="headerlink" href="#re.X" title="Permalink to this definition">¶</a></dt>
<dt id="re.VERBOSE">
<code class="descclassname">re.</code><code class="descname">VERBOSE</code><a class="headerlink" href="#re.VERBOSE" title="Permalink to this definition">¶</a></dt>
<dd><p>This flag allows you to write regular expressions that look nicer and are
more readable by allowing you to visually separate logical sections of the
pattern and add comments. Whitespace within the pattern is ignored, except
when in a character class, or when preceded by an unescaped backslash,
or within tokens like <code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">(?:</span></code> or <code class="docutils literal notranslate"><span class="pre">(?P<...></span></code>.
When a line contains a <code class="docutils literal notranslate"><span class="pre">#</span></code> that is not in a character class and is not
preceded by an unescaped backslash, all characters from the leftmost such
<code class="docutils literal notranslate"><span class="pre">#</span></code> through the end of the line are ignored.</p>
<p>This means that the two following regular expression objects that match a
decimal number are functionally equal:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">a</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"""\d + # the integral part</span>
<span class="s2"> \. # the decimal point</span>
<span class="s2"> \d * # some fractional digits"""</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">X</span><span class="p">)</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\d+\.\d*"</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="re.search">
<code class="descclassname">re.</code><code class="descname">search</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.search" title="Permalink to this definition">¶</a></dt>
<dd><p>Scan through <em>string</em> looking for the first location where the regular expression
<em>pattern</em> produces a match, and return a corresponding <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a>
instance. Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if no position in the string matches the pattern; note
that this is different from finding a zero-length match at some point in the
string.</p>
</dd></dl>
<dl class="function">
<dt id="re.match">
<code class="descclassname">re.</code><code class="descname">match</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match" title="Permalink to this definition">¶</a></dt>
<dd><p>If zero or more characters at the beginning of <em>string</em> match the regular
expression <em>pattern</em>, return a corresponding <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> instance.
Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if the string does not match the pattern; note that this is
different from a zero-length match.</p>
<p>Note that even in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode, <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> will only match
at the beginning of the string and not at the beginning of each line.</p>
<p>If you want to locate a match anywhere in <em>string</em>, use <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a>
instead (see also <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a>).</p>
</dd></dl>
<dl class="function">
<dt id="re.split">
<code class="descclassname">re.</code><code class="descname">split</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>maxsplit=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.split" title="Permalink to this definition">¶</a></dt>
<dd><p>Split <em>string</em> by the occurrences of <em>pattern</em>. If capturing parentheses are
used in <em>pattern</em>, then the text of all groups in the pattern are also returned
as part of the resulting list. If <em>maxsplit</em> is nonzero, at most <em>maxsplit</em>
splits occur, and the remainder of the string is returned as the final element
of the list. (Incompatibility note: in the original Python 1.5 release,
<em>maxsplit</em> was ignored. This has been fixed in later releases.)</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'\W+'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">)</span>
<span class="go">['Words', 'words', 'words', '']</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'(\W+)'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">)</span>
<span class="go">['Words', ', ', 'words', ', ', 'words', '.', '']</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'\W+'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="go">['Words', 'words, words.']</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'[a-f]+'</span><span class="p">,</span> <span class="s1">'0a3B9'</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
<span class="go">['0', '3', '9']</span>
</pre></div>
</div>
<p>If there are capturing groups in the separator and it matches at the start of
the string, the result will start with an empty string. The same holds for
the end of the string:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'(\W+)'</span><span class="p">,</span> <span class="s1">'...words, words...'</span><span class="p">)</span>
<span class="go">['', '...', 'words', ', ', 'words', '...', '']</span>
</pre></div>
</div>
<p>That way, separator components are always found at the same relative
indices within the result list (e.g., if there’s one capturing group
in the separator, the 0th, the 2nd and so forth).</p>
<p>Note that <em>split</em> will never split a string on an empty pattern match.
For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'x*'</span><span class="p">,</span> <span class="s1">'foo'</span><span class="p">)</span>
<span class="go">['foo']</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">"(?m)^$"</span><span class="p">,</span> <span class="s2">"foo</span><span class="se">\n\n</span><span class="s2">bar</span><span class="se">\n</span><span class="s2">"</span><span class="p">)</span>
<span class="go">['foo\n\nbar\n']</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.7: </span>Added the optional flags argument.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="re.findall">
<code class="descclassname">re.</code><code class="descname">findall</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.findall" title="Permalink to this definition">¶</a></dt>
<dd><p>Return all non-overlapping matches of <em>pattern</em> in <em>string</em>, as a list of
strings. The <em>string</em> is scanned left-to-right, and matches are returned in
the order found. If one or more groups are present in the pattern, return a
list of groups; this will be a list of tuples if the pattern has more than
one group. Empty matches are included in the result.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Due to the limitation of the current implementation the character
following an empty match is not included in a next match, so
<code class="docutils literal notranslate"><span class="pre">findall(r'^|\w+',</span> <span class="pre">'two</span> <span class="pre">words')</span></code> returns <code class="docutils literal notranslate"><span class="pre">['',</span> <span class="pre">'wo',</span> <span class="pre">'words']</span></code>
(note missed “t”). This is changed in Python 3.7.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 1.5.2.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.4: </span>Added the optional flags argument.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="re.finditer">
<code class="descclassname">re.</code><code class="descname">finditer</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.finditer" title="Permalink to this definition">¶</a></dt>
<dd><p>Return an <a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> yielding <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> instances over all
non-overlapping matches for the RE <em>pattern</em> in <em>string</em>. The <em>string</em> is
scanned left-to-right, and matches are returned in the order found. Empty
matches are included in the result. See also the note about <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.2.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.4: </span>Added the optional flags argument.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="re.sub">
<code class="descclassname">re.</code><code class="descname">sub</code><span class="sig-paren">(</span><em>pattern</em>, <em>repl</em>, <em>string</em>, <em>count=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.sub" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the string obtained by replacing the leftmost non-overlapping occurrences
of <em>pattern</em> in <em>string</em> by the replacement <em>repl</em>. If the pattern isn’t found,
<em>string</em> is returned unchanged. <em>repl</em> can be a string or a function; if it is
a string, any backslash escapes in it are processed. That is, <code class="docutils literal notranslate"><span class="pre">\n</span></code> is
converted to a single newline character, <code class="docutils literal notranslate"><span class="pre">\r</span></code> is converted to a carriage return, and
so forth. Unknown escapes such as <code class="docutils literal notranslate"><span class="pre">\j</span></code> are left alone. Backreferences, such
as <code class="docutils literal notranslate"><span class="pre">\6</span></code>, are replaced with the substring matched by group 6 in the pattern.
For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):'</span><span class="p">,</span>
<span class="gp">... </span> <span class="sa">r</span><span class="s1">'static PyObject*\npy_\1(void)\n{'</span><span class="p">,</span>
<span class="gp">... </span> <span class="s1">'def myfunc():'</span><span class="p">)</span>
<span class="go">'static PyObject*\npy_myfunc(void)\n{'</span>
</pre></div>
</div>
<p>If <em>repl</em> is a function, it is called for every non-overlapping occurrence of
<em>pattern</em>. The function takes a single match object argument, and returns the
replacement string. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">dashrepl</span><span class="p">(</span><span class="n">matchobj</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">matchobj</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="o">==</span> <span class="s1">'-'</span><span class="p">:</span> <span class="k">return</span> <span class="s1">' '</span>
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span> <span class="k">return</span> <span class="s1">'-'</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="s1">'-{1,2}'</span><span class="p">,</span> <span class="n">dashrepl</span><span class="p">,</span> <span class="s1">'pro----gram-files'</span><span class="p">)</span>
<span class="go">'pro--gram files'</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\sAND\s'</span><span class="p">,</span> <span class="s1">' & '</span><span class="p">,</span> <span class="s1">'Baked Beans And Spam'</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
<span class="go">'Baked Beans & Spam'</span>
</pre></div>
</div>
<p>The pattern may be a string or an RE object.</p>
<p>The optional argument <em>count</em> is the maximum number of pattern occurrences to be
replaced; <em>count</em> must be a non-negative integer. If omitted or zero, all
occurrences will be replaced. Empty matches for the pattern are replaced only
when not adjacent to a previous match, so <code class="docutils literal notranslate"><span class="pre">sub('x*',</span> <span class="pre">'-',</span> <span class="pre">'abc')</span></code> returns
<code class="docutils literal notranslate"><span class="pre">'-a-b-c-'</span></code>.</p>
<p>In string-type <em>repl</em> arguments, in addition to the character escapes and
backreferences described above,
<code class="docutils literal notranslate"><span class="pre">\g<name></span></code> will use the substring matched by the group named <code class="docutils literal notranslate"><span class="pre">name</span></code>, as
defined by the <code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code> syntax. <code class="docutils literal notranslate"><span class="pre">\g<number></span></code> uses the corresponding
group number; <code class="docutils literal notranslate"><span class="pre">\g<2></span></code> is therefore equivalent to <code class="docutils literal notranslate"><span class="pre">\2</span></code>, but isn’t ambiguous
in a replacement such as <code class="docutils literal notranslate"><span class="pre">\g<2>0</span></code>. <code class="docutils literal notranslate"><span class="pre">\20</span></code> would be interpreted as a
reference to group 20, not a reference to group 2 followed by the literal
character <code class="docutils literal notranslate"><span class="pre">'0'</span></code>. The backreference <code class="docutils literal notranslate"><span class="pre">\g<0></span></code> substitutes in the entire
substring matched by the RE.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.7: </span>Added the optional flags argument.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="re.subn">
<code class="descclassname">re.</code><code class="descname">subn</code><span class="sig-paren">(</span><em>pattern</em>, <em>repl</em>, <em>string</em>, <em>count=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.subn" title="Permalink to this definition">¶</a></dt>
<dd><p>Perform the same operation as <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a>, but return a tuple <code class="docutils literal notranslate"><span class="pre">(new_string,</span>
<span class="pre">number_of_subs_made)</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.7: </span>Added the optional flags argument.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="re.escape">
<code class="descclassname">re.</code><code class="descname">escape</code><span class="sig-paren">(</span><em>pattern</em><span class="sig-paren">)</span><a class="headerlink" href="#re.escape" title="Permalink to this definition">¶</a></dt>
<dd><p>Escape all the characters in <em>pattern</em> except ASCII letters and numbers.
This is useful if you want to match an arbitrary literal string that may
have regular expression metacharacters in it. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span> <span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="s1">'python.exe'</span><span class="p">)</span>
<span class="go">python\.exe</span>
<span class="gp">>>> </span><span class="n">legal_chars</span> <span class="o">=</span> <span class="n">string</span><span class="o">.</span><span class="n">ascii_lowercase</span> <span class="o">+</span> <span class="n">string</span><span class="o">.</span><span class="n">digits</span> <span class="o">+</span> <span class="s2">"!#$%&'*+-.^_`|~:"</span>
<span class="gp">>>> </span><span class="nb">print</span> <span class="s1">'[</span><span class="si">%s</span><span class="s1">]+'</span> <span class="o">%</span> <span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="n">legal_chars</span><span class="p">)</span>
<span class="go">[abcdefghijklmnopqrstuvwxyz0123456789\!\#\$\%\&\'\*\+\-\.\^\_\`\|\~\:]+</span>
<span class="gp">>>> </span><span class="n">operators</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'+'</span><span class="p">,</span> <span class="s1">'-'</span><span class="p">,</span> <span class="s1">'*'</span><span class="p">,</span> <span class="s1">'/'</span><span class="p">,</span> <span class="s1">'**'</span><span class="p">]</span>
<span class="gp">>>> </span><span class="nb">print</span> <span class="s1">'|'</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">,</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">operators</span><span class="p">,</span> <span class="n">reverse</span><span class="o">=</span><span class="kc">True</span><span class="p">)))</span>
<span class="go">\/|\-|\+|\*\*|\*</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="re.purge">
<code class="descclassname">re.</code><code class="descname">purge</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#re.purge" title="Permalink to this definition">¶</a></dt>
<dd><p>Clear the regular expression cache.</p>
</dd></dl>
<dl class="exception">
<dt id="re.error">
<em class="property">exception </em><code class="descclassname">re.</code><code class="descname">error</code><a class="headerlink" href="#re.error" title="Permalink to this definition">¶</a></dt>
<dd><p>Exception raised when a string passed to one of the functions here is not a
valid regular expression (for example, it might contain unmatched parentheses)
or when some other error occurs during compilation or matching. It is never an
error if a string contains no match for a pattern.</p>
</dd></dl>
</div>
<div class="section" id="regular-expression-objects">
<span id="re-objects"></span><h2>7.2.3. Regular Expression Objects<a class="headerlink" href="#regular-expression-objects" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="re.RegexObject">
<em class="property">class </em><code class="descclassname">re.</code><code class="descname">RegexObject</code><a class="headerlink" href="#re.RegexObject" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#re.RegexObject" title="re.RegexObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">RegexObject</span></code></a> class supports the following methods and attributes:</p>
<dl class="method">
<dt id="re.RegexObject.search">
<code class="descname">search</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.search" title="Permalink to this definition">¶</a></dt>
<dd><p>Scan through <em>string</em> looking for a location where this regular expression
produces a match, and return a corresponding <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> instance.
Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if no position in the string matches the pattern; note that this
is different from finding a zero-length match at some point in the string.</p>
<p>The optional second parameter <em>pos</em> gives an index in the string where the
search is to start; it defaults to <code class="docutils literal notranslate"><span class="pre">0</span></code>. This is not completely equivalent to
slicing the string; the <code class="docutils literal notranslate"><span class="pre">'^'</span></code> pattern character matches at the real beginning
of the string and at positions just after a newline, but not necessarily at the
index where the search is to start.</p>
<p>The optional parameter <em>endpos</em> limits how far the string will be searched; it
will be as if the string is <em>endpos</em> characters long, so only the characters
from <em>pos</em> to <code class="docutils literal notranslate"><span class="pre">endpos</span> <span class="pre">-</span> <span class="pre">1</span></code> will be searched for a match. If <em>endpos</em> is less
than <em>pos</em>, no match will be found, otherwise, if <em>rx</em> is a compiled regular
expression object, <code class="docutils literal notranslate"><span class="pre">rx.search(string,</span> <span class="pre">0,</span> <span class="pre">50)</span></code> is equivalent to
<code class="docutils literal notranslate"><span class="pre">rx.search(string[:50],</span> <span class="pre">0)</span></code>.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"d"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">)</span> <span class="c1"># Match at index 0</span>
<span class="go"><_sre.SRE_Match object at ...></span>
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># No match; search doesn't include the "d"</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.match">
<code class="descname">match</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.match" title="Permalink to this definition">¶</a></dt>
<dd><p>If zero or more characters at the <em>beginning</em> of <em>string</em> match this regular
expression, return a corresponding <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> instance. Return
<code class="docutils literal notranslate"><span class="pre">None</span></code> if the string does not match the pattern; note that this is different
from a zero-length match.</p>
<p>The optional <em>pos</em> and <em>endpos</em> parameters have the same meaning as for the
<a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> method.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"o"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">)</span> <span class="c1"># No match as "o" is not at the start of "dog".</span>
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># Match as "o" is the 2nd character of "dog".</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
<p>If you want to locate a match anywhere in <em>string</em>, use
<a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> instead (see also <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a>).</p>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.split">
<code class="descname">split</code><span class="sig-paren">(</span><em>string</em>, <em>maxsplit=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.split" title="Permalink to this definition">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.findall">
<code class="descname">findall</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.findall" title="Permalink to this definition">¶</a></dt>
<dd><p>Similar to the <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> function, using the compiled pattern, but
also accepts optional <em>pos</em> and <em>endpos</em> parameters that limit the search
region like for <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a>.</p>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.finditer">
<code class="descname">finditer</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.finditer" title="Permalink to this definition">¶</a></dt>
<dd><p>Similar to the <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> function, using the compiled pattern, but
also accepts optional <em>pos</em> and <em>endpos</em> parameters that limit the search
region like for <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a>.</p>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.sub">
<code class="descname">sub</code><span class="sig-paren">(</span><em>repl</em>, <em>string</em>, <em>count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.sub" title="Permalink to this definition">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>
<dl class="method">
<dt id="re.RegexObject.subn">
<code class="descname">subn</code><span class="sig-paren">(</span><em>repl</em>, <em>string</em>, <em>count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.RegexObject.subn" title="Permalink to this definition">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">subn()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.RegexObject.flags">
<code class="descname">flags</code><a class="headerlink" href="#re.RegexObject.flags" title="Permalink to this definition">¶</a></dt>
<dd><p>The regex matching flags. This is a combination of the flags given to
<a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">compile()</span></code></a> and any <code class="docutils literal notranslate"><span class="pre">(?...)</span></code> inline flags in the pattern.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.RegexObject.groups">
<code class="descname">groups</code><a class="headerlink" href="#re.RegexObject.groups" title="Permalink to this definition">¶</a></dt>
<dd><p>The number of capturing groups in the pattern.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.RegexObject.groupindex">
<code class="descname">groupindex</code><a class="headerlink" href="#re.RegexObject.groupindex" title="Permalink to this definition">¶</a></dt>
<dd><p>A dictionary mapping any symbolic group names defined by <code class="docutils literal notranslate"><span class="pre">(?P<id>)</span></code> to group
numbers. The dictionary is empty if no symbolic groups were used in the
pattern.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.RegexObject.pattern">
<code class="descname">pattern</code><a class="headerlink" href="#re.RegexObject.pattern" title="Permalink to this definition">¶</a></dt>
<dd><p>The pattern string from which the RE object was compiled.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="match-objects">
<span id="id1"></span><h2>7.2.4. Match Objects<a class="headerlink" href="#match-objects" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="re.MatchObject">
<em class="property">class </em><code class="descclassname">re.</code><code class="descname">MatchObject</code><a class="headerlink" href="#re.MatchObject" title="Permalink to this definition">¶</a></dt>
<dd><p>Match objects always have a boolean value of <code class="docutils literal notranslate"><span class="pre">True</span></code>.
Since <code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code> return <code class="docutils literal notranslate"><span class="pre">None</span></code>
when there is no match, you can test whether there was a match with a simple
<code class="docutils literal notranslate"><span class="pre">if</span></code> statement:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">match</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
<span class="k">if</span> <span class="n">match</span><span class="p">:</span>
<span class="n">process</span><span class="p">(</span><span class="n">match</span><span class="p">)</span>
</pre></div>
</div>
<p>Match objects support the following methods and attributes:</p>
<dl class="method">
<dt id="re.MatchObject.expand">
<code class="descname">expand</code><span class="sig-paren">(</span><em>template</em><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.expand" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the string obtained by doing backslash substitution on the template
string <em>template</em>, as done by the <a class="reference internal" href="#re.RegexObject.sub" title="re.RegexObject.sub"><code class="xref py py-meth docutils literal notranslate"><span class="pre">sub()</span></code></a> method. Escapes
such as <code class="docutils literal notranslate"><span class="pre">\n</span></code> are converted to the appropriate characters, and numeric
backreferences (<code class="docutils literal notranslate"><span class="pre">\1</span></code>, <code class="docutils literal notranslate"><span class="pre">\2</span></code>) and named backreferences (<code class="docutils literal notranslate"><span class="pre">\g<1></span></code>,
<code class="docutils literal notranslate"><span class="pre">\g<name></span></code>) are replaced by the contents of the corresponding group.</p>
</dd></dl>
<dl class="method">
<dt id="re.MatchObject.group">
<code class="descname">group</code><span class="sig-paren">(</span><span class="optional">[</span><em>group1</em>, <em>...</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.group" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns one or more subgroups of the match. If there is a single argument, the
result is a single string; if there are multiple arguments, the result is a
tuple with one item per argument. Without arguments, <em>group1</em> defaults to zero
(the whole match is returned). If a <em>groupN</em> argument is zero, the corresponding
return value is the entire matching string; if it is in the inclusive range
[1..99], it is the string matching the corresponding parenthesized group. If a
group number is negative or larger than the number of groups defined in the
pattern, an <a class="reference internal" href="exceptions.html#exceptions.IndexError" title="exceptions.IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> exception is raised. If a group is contained in a
part of the pattern that did not match, the corresponding result is <code class="docutils literal notranslate"><span class="pre">None</span></code>.
If a group is contained in a part of the pattern that matched multiple times,
the last match is returned.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w+) (\w+)"</span><span class="p">,</span> <span class="s2">"Isaac Newton, physicist"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="c1"># The entire match</span>
<span class="go">'Isaac Newton'</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="c1"># The first parenthesized subgroup.</span>
<span class="go">'Isaac'</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span> <span class="c1"># The second parenthesized subgroup.</span>
<span class="go">'Newton'</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span> <span class="c1"># Multiple arguments give us a tuple.</span>
<span class="go">('Isaac', 'Newton')</span>
</pre></div>
</div>
<p>If the regular expression uses the <code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code> syntax, the <em>groupN</em>
arguments may also be strings identifying groups by their group name. If a
string argument is not used as a group name in the pattern, an <a class="reference internal" href="exceptions.html#exceptions.IndexError" title="exceptions.IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a>
exception is raised.</p>
<p>A moderately complicated example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(?P<first_name>\w+) (?P<last_name>\w+)"</span><span class="p">,</span> <span class="s2">"Malcolm Reynolds"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">'first_name'</span><span class="p">)</span>
<span class="go">'Malcolm'</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">'last_name'</span><span class="p">)</span>
<span class="go">'Reynolds'</span>
</pre></div>
</div>
<p>Named groups can also be referred to by their index:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">'Malcolm'</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="go">'Reynolds'</span>
</pre></div>
</div>
<p>If a group matches multiple times, only the last match is accessible:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(..)+"</span><span class="p">,</span> <span class="s2">"a1b2c3"</span><span class="p">)</span> <span class="c1"># Matches 3 times.</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="c1"># Returns only the last match.</span>
<span class="go">'c3'</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="re.MatchObject.groups">
<code class="descname">groups</code><span class="sig-paren">(</span><span class="optional">[</span><em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.groups" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a tuple containing all the subgroups of the match, from 1 up to however
many groups are in the pattern. The <em>default</em> argument is used for groups that
did not participate in the match; it defaults to <code class="docutils literal notranslate"><span class="pre">None</span></code>. (Incompatibility
note: in the original Python 1.5 release, if the tuple was one element long, a
string would be returned instead. In later versions (from 1.5.1 on), a
singleton tuple is returned in such cases.)</p>
<p>For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\d+)\.(\d+)"</span><span class="p">,</span> <span class="s2">"24.1632"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span>
<span class="go">('24', '1632')</span>
</pre></div>
</div>
<p>If we make the decimal place and everything after it optional, not all groups
might participate in the match. These groups will default to <code class="docutils literal notranslate"><span class="pre">None</span></code> unless
the <em>default</em> argument is given:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\d+)\.?(\d+)?"</span><span class="p">,</span> <span class="s2">"24"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span> <span class="c1"># Second group defaults to None.</span>
<span class="go">('24', None)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">(</span><span class="s1">'0'</span><span class="p">)</span> <span class="c1"># Now, the second group defaults to '0'.</span>
<span class="go">('24', '0')</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="re.MatchObject.groupdict">
<code class="descname">groupdict</code><span class="sig-paren">(</span><span class="optional">[</span><em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.groupdict" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a dictionary containing all the <em>named</em> subgroups of the match, keyed by
the subgroup name. The <em>default</em> argument is used for groups that did not
participate in the match; it defaults to <code class="docutils literal notranslate"><span class="pre">None</span></code>. For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(?P<first_name>\w+) (?P<last_name>\w+)"</span><span class="p">,</span> <span class="s2">"Malcolm Reynolds"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groupdict</span><span class="p">()</span>
<span class="go">{'first_name': 'Malcolm', 'last_name': 'Reynolds'}</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="re.MatchObject.start">
<code class="descname">start</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.start" title="Permalink to this definition">¶</a></dt>
<dt id="re.MatchObject.end">
<code class="descname">end</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.end" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the indices of the start and end of the substring matched by <em>group</em>;
<em>group</em> defaults to zero (meaning the whole matched substring). Return <code class="docutils literal notranslate"><span class="pre">-1</span></code> if
<em>group</em> exists but did not contribute to the match. For a match object <em>m</em>, and
a group <em>g</em> that did contribute to the match, the substring matched by group <em>g</em>
(equivalent to <code class="docutils literal notranslate"><span class="pre">m.group(g)</span></code>) is</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">m</span><span class="o">.</span><span class="n">string</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(</span><span class="n">g</span><span class="p">):</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(</span><span class="n">g</span><span class="p">)]</span>
</pre></div>
</div>
<p>Note that <code class="docutils literal notranslate"><span class="pre">m.start(group)</span></code> will equal <code class="docutils literal notranslate"><span class="pre">m.end(group)</span></code> if <em>group</em> matched a
null string. For example, after <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">=</span> <span class="pre">re.search('b(c?)',</span> <span class="pre">'cba')</span></code>,
<code class="docutils literal notranslate"><span class="pre">m.start(0)</span></code> is 1, <code class="docutils literal notranslate"><span class="pre">m.end(0)</span></code> is 2, <code class="docutils literal notranslate"><span class="pre">m.start(1)</span></code> and <code class="docutils literal notranslate"><span class="pre">m.end(1)</span></code> are both
2, and <code class="docutils literal notranslate"><span class="pre">m.start(2)</span></code> raises an <a class="reference internal" href="exceptions.html#exceptions.IndexError" title="exceptions.IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> exception.</p>
<p>An example that will remove <em>remove_this</em> from email addresses:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">email</span> <span class="o">=</span> <span class="s2">"tony@tiremove_thisger.net"</span>
<span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"remove_this"</span><span class="p">,</span> <span class="n">email</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">email</span><span class="p">[:</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">()]</span> <span class="o">+</span> <span class="n">email</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">():]</span>
<span class="go">'tony@tiger.net'</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="re.MatchObject.span">
<code class="descname">span</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.MatchObject.span" title="Permalink to this definition">¶</a></dt>
<dd><p>For <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> <em>m</em>, return the 2-tuple <code class="docutils literal notranslate"><span class="pre">(m.start(group),</span>
<span class="pre">m.end(group))</span></code>. Note that if <em>group</em> did not contribute to the match, this is
<code class="docutils literal notranslate"><span class="pre">(-1,</span> <span class="pre">-1)</span></code>. <em>group</em> defaults to zero, the entire match.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.pos">
<code class="descname">pos</code><a class="headerlink" href="#re.MatchObject.pos" title="Permalink to this definition">¶</a></dt>
<dd><p>The value of <em>pos</em> which was passed to the <a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> or
<a class="reference internal" href="#re.RegexObject.match" title="re.RegexObject.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> method of the <a class="reference internal" href="#re.RegexObject" title="re.RegexObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">RegexObject</span></code></a>. This is the
index into the string at which the RE engine started looking for a match.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.endpos">
<code class="descname">endpos</code><a class="headerlink" href="#re.MatchObject.endpos" title="Permalink to this definition">¶</a></dt>
<dd><p>The value of <em>endpos</em> which was passed to the <a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> or
<a class="reference internal" href="#re.RegexObject.match" title="re.RegexObject.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> method of the <a class="reference internal" href="#re.RegexObject" title="re.RegexObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">RegexObject</span></code></a>. This is the
index into the string beyond which the RE engine will not go.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.lastindex">
<code class="descname">lastindex</code><a class="headerlink" href="#re.MatchObject.lastindex" title="Permalink to this definition">¶</a></dt>
<dd><p>The integer index of the last matched capturing group, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if no group
was matched at all. For example, the expressions <code class="docutils literal notranslate"><span class="pre">(a)b</span></code>, <code class="docutils literal notranslate"><span class="pre">((a)(b))</span></code>, and
<code class="docutils literal notranslate"><span class="pre">((ab))</span></code> will have <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">1</span></code> if applied to the string <code class="docutils literal notranslate"><span class="pre">'ab'</span></code>, while
the expression <code class="docutils literal notranslate"><span class="pre">(a)(b)</span></code> will have <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">2</span></code>, if applied to the same
string.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.lastgroup">
<code class="descname">lastgroup</code><a class="headerlink" href="#re.MatchObject.lastgroup" title="Permalink to this definition">¶</a></dt>
<dd><p>The name of the last matched capturing group, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the group didn’t
have a name, or if no group was matched at all.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.re">
<code class="descname">re</code><a class="headerlink" href="#re.MatchObject.re" title="Permalink to this definition">¶</a></dt>
<dd><p>The regular expression object whose <a class="reference internal" href="#re.RegexObject.match" title="re.RegexObject.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> or
<a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> method produced this <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a>
instance.</p>
</dd></dl>
<dl class="attribute">
<dt id="re.MatchObject.string">
<code class="descname">string</code><a class="headerlink" href="#re.MatchObject.string" title="Permalink to this definition">¶</a></dt>
<dd><p>The string passed to <a class="reference internal" href="#re.RegexObject.match" title="re.RegexObject.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> or
<a class="reference internal" href="#re.RegexObject.search" title="re.RegexObject.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="examples">
<h2>7.2.5. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="checking-for-a-pair">
<h3>7.2.5.1. Checking For a Pair<a class="headerlink" href="#checking-for-a-pair" title="Permalink to this headline">¶</a></h3>
<p>In this example, we’ll use the following helper function to display match
objects a little more gracefully:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">displaymatch</span><span class="p">(</span><span class="n">match</span><span class="p">):</span>
<span class="k">if</span> <span class="n">match</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="k">return</span> <span class="bp">None</span>
<span class="k">return</span> <span class="s1">'<Match: </span><span class="si">%r</span><span class="s1">, groups=</span><span class="si">%r</span><span class="s1">>'</span> <span class="o">%</span> <span class="p">(</span><span class="n">match</span><span class="o">.</span><span class="n">group</span><span class="p">(),</span> <span class="n">match</span><span class="o">.</span><span class="n">groups</span><span class="p">())</span>
</pre></div>
</div>
<p>Suppose you are writing a poker program where a player’s hand is represented as
a 5-character string with each character representing a card, “a” for ace, “k”
for king, “q” for queen, “j” for jack, “t” for 10, and “2” through “9”
representing the card with that value.</p>
<p>To see if a given string is a valid hand, one could do the following:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"^[a2-9tjqk]</span><span class="si">{5}</span><span class="s2">$"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt5q"</span><span class="p">))</span> <span class="c1"># Valid.</span>
<span class="go">"<Match: 'akt5q', groups=()>"</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt5e"</span><span class="p">))</span> <span class="c1"># Invalid.</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt"</span><span class="p">))</span> <span class="c1"># Invalid.</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"727ak"</span><span class="p">))</span> <span class="c1"># Valid.</span>
<span class="go">"<Match: '727ak', groups=()>"</span>
</pre></div>
</div>
<p>That last hand, <code class="docutils literal notranslate"><span class="pre">"727ak"</span></code>, contained a pair, or two of the same valued cards.
To match this with a regular expression, one could use backreferences as such:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pair</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">".*(.).*\1"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"717ak"</span><span class="p">))</span> <span class="c1"># Pair of 7s.</span>
<span class="go">"<Match: '717', groups=('7',)>"</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"718ak"</span><span class="p">))</span> <span class="c1"># No pairs.</span>
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"354aa"</span><span class="p">))</span> <span class="c1"># Pair of aces.</span>
<span class="go">"<Match: '354aa', groups=('a',)>"</span>
</pre></div>
</div>
<p>To find out what card the pair consists of, one could use the
<a class="reference internal" href="#re.MatchObject.group" title="re.MatchObject.group"><code class="xref py py-meth docutils literal notranslate"><span class="pre">group()</span></code></a> method of <a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> in the following
manner:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"717ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">'7'</span>
<span class="go"># Error because re.match() returns None, which doesn't have a group() method:</span>
<span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"718ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
File <span class="nb">"<pyshell#23>"</span>, line <span class="m">1</span>, in <span class="n"><module></span>
<span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">".*(.).*\1"</span><span class="p">,</span> <span class="s2">"718ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gr">AttributeError</span>: <span class="n">'NoneType' object has no attribute 'group'</span>
<span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"354aa"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">'a'</span>
</pre></div>
</div>
</div>
<div class="section" id="simulating-scanf">
<h3>7.2.5.2. Simulating scanf()<a class="headerlink" href="#simulating-scanf" title="Permalink to this headline">¶</a></h3>
<p id="index-0">Python does not currently have an equivalent to <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code>. Regular
expressions are generally more powerful, though also more verbose, than
<code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format strings. The table below offers some more-or-less
equivalent mappings between <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format tokens and regular
expressions.</p>
<table border="1" class="docutils">
<colgroup>
<col width="42%" />
<col width="58%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head"><code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> Token</th>
<th class="head">Regular Expression</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%c</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">.</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%5c</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">.{5}</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%d</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?\d+</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%e</span></code>, <code class="docutils literal notranslate"><span class="pre">%E</span></code>, <code class="docutils literal notranslate"><span class="pre">%f</span></code>, <code class="docutils literal notranslate"><span class="pre">%g</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%i</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%o</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?[0-7]+</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%s</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">\S+</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%u</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">\d+</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%x</span></code>, <code class="docutils literal notranslate"><span class="pre">%X</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX])?[\dA-Fa-f]+</span></code></td>
</tr>
</tbody>
</table>
<p>To extract the filename and numbers from a string like</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">sbin</span><span class="o">/</span><span class="n">sendmail</span> <span class="o">-</span> <span class="mi">0</span> <span class="n">errors</span><span class="p">,</span> <span class="mi">4</span> <span class="n">warnings</span>
</pre></div>
</div>
<p>you would use a <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format like</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">%</span><span class="n">s</span> <span class="o">-</span> <span class="o">%</span><span class="n">d</span> <span class="n">errors</span><span class="p">,</span> <span class="o">%</span><span class="n">d</span> <span class="n">warnings</span>
</pre></div>
</div>
<p>The equivalent regular expression would be</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">(</span>\<span class="n">S</span><span class="o">+</span><span class="p">)</span> <span class="o">-</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">errors</span><span class="p">,</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">warnings</span>
</pre></div>
</div>
</div>
<div class="section" id="search-vs-match">
<span id="id2"></span><h3>7.2.5.3. search() vs. match()<a class="headerlink" href="#search-vs-match" title="Permalink to this headline">¶</a></h3>
<p>Python offers two different primitive operations based on regular expressions:
<a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> checks for a match only at the beginning of the string, while
<a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.search()</span></code></a> checks for a match anywhere in the string (this is what Perl
does by default).</p>
<p>For example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># Match</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
<p>Regular expressions beginning with <code class="docutils literal notranslate"><span class="pre">'^'</span></code> can be used with <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> to
restrict the match at the beginning of the string:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"^c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"^a"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># Match</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
<p>Note however that in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> only matches at the
beginning of the string, whereas using <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> with a regular expression
beginning with <code class="docutils literal notranslate"><span class="pre">'^'</span></code> will match at the beginning of each line.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'X'</span><span class="p">,</span> <span class="s1">'A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X'</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span> <span class="c1"># No match</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'^X'</span><span class="p">,</span> <span class="s1">'A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X'</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span> <span class="c1"># Match</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
</div>
<div class="section" id="making-a-phonebook">
<h3>7.2.5.4. Making a Phonebook<a class="headerlink" href="#making-a-phonebook" title="Permalink to this headline">¶</a></h3>
<p><a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> splits a string into a list delimited by the passed pattern. The
method is invaluable for converting textual data into data structures that can be
easily read and modified by Python as demonstrated in the following example that
creates a phonebook.</p>
<p>First, here is the input. Normally it may come from a file, here we are using
triple-quoted string syntax:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"""Ross McFluff: 834.345.1254 155 Elm Street</span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">... </span><span class="s2">Ronald Heathmore: 892.345.3428 436 Finley Avenue</span>
<span class="gp">... </span><span class="s2">Frank Burger: 925.541.7625 662 South Dogwood Way</span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">... </span><span class="s2">Heather Albrecht: 548.326.4584 919 Park Place"""</span>
</pre></div>
</div>
<p>The entries are separated by one or more newlines. Now we convert the string
into a list with each nonempty line having its own entry:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">entries</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">+"</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">entries</span>
<span class="go">['Ross McFluff: 834.345.1254 155 Elm Street',</span>
<span class="go">'Ronald Heathmore: 892.345.3428 436 Finley Avenue',</span>
<span class="go">'Frank Burger: 925.541.7625 662 South Dogwood Way',</span>
<span class="go">'Heather Albrecht: 548.326.4584 919 Park Place']</span>
</pre></div>
</div>
<p>Finally, split each entry into a list with first name, last name, telephone
number, and address. We use the <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> parameter of <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a>
because the address has spaces, our splitting pattern, in it:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">":? "</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
<span class="go">[['Ross', 'McFluff', '834.345.1254', '155 Elm Street'],</span>
<span class="go">['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'],</span>
<span class="go">['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'],</span>
<span class="go">['Heather', 'Albrecht', '548.326.4584', '919 Park Place']]</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">:?</span></code> pattern matches the colon after the last name, so that it does not
occur in the result list. With a <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> of <code class="docutils literal notranslate"><span class="pre">4</span></code>, we could separate the
house number from the street name:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">":? "</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
<span class="go">[['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'],</span>
<span class="go">['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'],</span>
<span class="go">['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'],</span>
<span class="go">['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']]</span>
</pre></div>
</div>
</div>
<div class="section" id="text-munging">
<h3>7.2.5.5. Text Munging<a class="headerlink" href="#text-munging" title="Permalink to this headline">¶</a></h3>
<p><a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> replaces every occurrence of a pattern with a string or the
result of a function. This example demonstrates using <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> with
a function to “munge” text, or randomize the order of all the characters
in each word of a sentence except for the first and last characters:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">repl</span><span class="p">(</span><span class="n">m</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">inner_word</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
<span class="gp">... </span> <span class="n">random</span><span class="o">.</span><span class="n">shuffle</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="s2">""</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span> <span class="o">+</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Professor Abdolmalek, please report your absences promptly."</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w)(\w+)(\w)"</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.'</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w)(\w+)(\w)"</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.'</span>
</pre></div>
</div>
</div>
<div class="section" id="finding-all-adverbs">
<h3>7.2.5.6. Finding all Adverbs<a class="headerlink" href="#finding-all-adverbs" title="Permalink to this headline">¶</a></h3>
<p><a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> matches <em>all</em> occurrences of a pattern, not just the first
one as <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> does. For example, if a writer wanted to
find all of the adverbs in some text, they might use <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> in
the following manner:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"He was carefully disguised but captured quickly by police."</span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\w+ly"</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">['carefully', 'quickly']</span>
</pre></div>
</div>
</div>
<div class="section" id="finding-all-adverbs-and-their-positions">
<h3>7.2.5.7. Finding all Adverbs and their Positions<a class="headerlink" href="#finding-all-adverbs-and-their-positions" title="Permalink to this headline">¶</a></h3>
<p>If one wants more information about all matches of a pattern than the matched
text, <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> is useful as it provides instances of
<a class="reference internal" href="#re.MatchObject" title="re.MatchObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">MatchObject</span></code></a> instead of strings. Continuing with the previous example,
if a writer wanted to find all of the adverbs <em>and their positions</em>
in some text, they would use <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> in the following manner:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"He was carefully disguised but captured quickly by police."</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">m</span> <span class="ow">in</span> <span class="n">re</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\w+ly"</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span> <span class="s1">'</span><span class="si">%02d</span><span class="s1">-</span><span class="si">%02d</span><span class="s1">: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">))</span>
<span class="go">07-16: carefully</span>
<span class="go">40-47: quickly</span>
</pre></div>
</div>
</div>
<div class="section" id="raw-string-notation">
<h3>7.2.5.8. Raw String Notation<a class="headerlink" href="#raw-string-notation" title="Permalink to this headline">¶</a></h3>
<p>Raw string notation (<code class="docutils literal notranslate"><span class="pre">r"text"</span></code>) keeps regular expressions sane. Without it,
every backslash (<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) in a regular expression would have to be prefixed with
another one to escape it. For example, the two following lines of code are
functionally identical:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\W(.)\1\W"</span><span class="p">,</span> <span class="s2">" ff "</span><span class="p">)</span>
<span class="go"><_sre.SRE_Match object at ...></span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"</span><span class="se">\\</span><span class="s2">W(.)</span><span class="se">\\</span><span class="s2">1</span><span class="se">\\</span><span class="s2">W"</span><span class="p">,</span> <span class="s2">" ff "</span><span class="p">)</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
<p>When one wants to match a literal backslash, it must be escaped in the regular
expression. With raw string notation, this means <code class="docutils literal notranslate"><span class="pre">r"\\"</span></code>. Without raw string
notation, one must use <code class="docutils literal notranslate"><span class="pre">"\\\\"</span></code>, making the following lines of code
functionally identical:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">,</span> <span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">)</span>
<span class="go"><_sre.SRE_Match object at ...></span>
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"</span><span class="se">\\\\</span><span class="s2">"</span><span class="p">,</span> <span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">)</span>
<span class="go"><_sre.SRE_Match object at ...></span>
</pre></div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">7.2. <code class="docutils literal notranslate"><span class="pre">re</span></code> — Regular expression operations</a><ul>
<li><a class="reference internal" href="#regular-expression-syntax">7.2.1. Regular Expression Syntax</a></li>
<li><a class="reference internal" href="#module-contents">7.2.2. Module Contents</a></li>
<li><a class="reference internal" href="#regular-expression-objects">7.2.3. Regular Expression Objects</a></li>
<li><a class="reference internal" href="#match-objects">7.2.4. Match Objects</a></li>
<li><a class="reference internal" href="#examples">7.2.5. Examples</a><ul>
<li><a class="reference internal" href="#checking-for-a-pair">7.2.5.1. Checking For a Pair</a></li>
<li><a class="reference internal" href="#simulating-scanf">7.2.5.2. Simulating scanf()</a></li>
<li><a class="reference internal" href="#search-vs-match">7.2.5.3. search() vs. match()</a></li>
<li><a class="reference internal" href="#making-a-phonebook">7.2.5.4. Making a Phonebook</a></li>
<li><a class="reference internal" href="#text-munging">7.2.5.5. Text Munging</a></li>
<li><a class="reference internal" href="#finding-all-adverbs">7.2.5.6. Finding all Adverbs</a></li>
<li><a class="reference internal" href="#finding-all-adverbs-and-their-positions">7.2.5.7. Finding all Adverbs and their Positions</a></li>
<li><a class="reference internal" href="#raw-string-notation">7.2.5.8. Raw String Notation</a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
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<h4>Next topic</h4>
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title="next chapter">7.3. <code class="docutils literal notranslate"><span class="pre">struct</span></code> — Interpret strings as packed binary data</a></p>
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