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<div class="section" id="module-csv">
<span id="csv-csv-file-reading-and-writing"></span><h1>13.1. <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> — CSV File Reading and Writing<a class="headerlink" href="#module-csv" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.3.</span></p>
</div>
<p id="index-0">The so-called CSV (Comma Separated Values) format is the most common import and
export format for spreadsheets and databases. There is no “CSV standard”, so
the format is operationally defined by the many applications which read and
write it. The lack of a standard means that subtle differences often exist in
the data produced and consumed by different applications. These differences can
make it annoying to process CSV files from multiple sources. Still, while the
delimiters and quoting characters vary, the overall format is similar enough
that it is possible to write a single module which can efficiently manipulate
such data, hiding the details of reading and writing the data from the
programmer.</p>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module implements classes to read and write tabular data in CSV
format. It allows programmers to say, “write this data in the format preferred
by Excel,” or “read data from this file which was generated by Excel,” without
knowing the precise details of the CSV format used by Excel. Programmers can
also describe the CSV formats understood by other applications or define their
own special-purpose CSV formats.</p>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module’s <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> and <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects read and
write sequences. Programmers can also read and write data in dictionary form
using the <a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictReader</span></code></a> and <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictWriter</span></code></a> classes.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This version of the <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module doesn’t support Unicode input. Also,
there are currently some issues regarding ASCII NUL characters. Accordingly,
all input should be UTF-8 or printable ASCII to be safe; see the examples in
section <a class="reference internal" href="#csv-examples"><span class="std std-ref">Examples</span></a>.</p>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><span class="target" id="index-1"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0305"><strong>PEP 305</strong></a> - CSV File API</dt>
<dd>The Python Enhancement Proposal which proposed this addition to Python.</dd>
</dl>
</div>
<div class="section" id="module-contents">
<span id="csv-contents"></span><h2>13.1.1. Module Contents<a class="headerlink" href="#module-contents" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module defines the following functions:</p>
<dl class="function">
<dt id="csv.reader">
<code class="descclassname">csv.</code><code class="descname">reader</code><span class="sig-paren">(</span><em>csvfile</em>, <em>dialect='excel'</em>, <em>**fmtparams</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.reader" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a reader object which will iterate over lines in the given <em>csvfile</em>.
<em>csvfile</em> can be any object which supports the <a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> protocol and returns a
string each time its <code class="xref py py-meth docutils literal notranslate"><span class="pre">next()</span></code> method is called — file objects and list
objects are both suitable. If <em>csvfile</em> is a file object, it must be opened
with the ‘b’ flag on platforms where that makes a difference. An optional
<em>dialect</em> parameter can be given which is used to define a set of parameters
specific to a particular CSV dialect. It may be an instance of a subclass of
the <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class or one of the strings returned by the
<a class="reference internal" href="#csv.list_dialects" title="csv.list_dialects"><code class="xref py py-func docutils literal notranslate"><span class="pre">list_dialects()</span></code></a> function. The other optional <em>fmtparams</em> keyword arguments
can be given to override individual formatting parameters in the current
dialect. For full details about the dialect and formatting parameters, see
section <a class="reference internal" href="#csv-fmt-params"><span class="std std-ref">Dialects and Formatting Parameters</span></a>.</p>
<p>Each row read from the csv file is returned as a list of strings. No
automatic data type conversion is performed.</p>
<p>A short usage example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">csv</span>
<span class="gp">>>> </span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'eggs.csv'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">csvfile</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">spamreader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">csvfile</span><span class="p">,</span> <span class="n">delimiter</span><span class="o">=</span><span class="s1">' '</span><span class="p">,</span> <span class="n">quotechar</span><span class="o">=</span><span class="s1">'|'</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">spamreader</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="n">row</span><span class="p">)</span>
<span class="go">Spam, Spam, Spam, Spam, Spam, Baked Beans</span>
<span class="go">Spam, Lovely Spam, Wonderful Spam</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.5: </span>The parser is now stricter with respect to multi-line quoted fields. Previously,
if a line ended within a quoted field without a terminating newline character, a
newline would be inserted into the returned field. This behavior caused problems
when reading files which contained carriage return characters within fields.
The behavior was changed to return the field without inserting newlines. As a
consequence, if newlines embedded within fields are important, the input should
be split into lines in a manner which preserves the newline characters.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="csv.writer">
<code class="descclassname">csv.</code><code class="descname">writer</code><span class="sig-paren">(</span><em>csvfile</em>, <em>dialect='excel'</em>, <em>**fmtparams</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.writer" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a writer object responsible for converting the user’s data into delimited
strings on the given file-like object. <em>csvfile</em> can be any object with a
<code class="xref py py-func docutils literal notranslate"><span class="pre">write()</span></code> method. If <em>csvfile</em> is a file object, it must be opened with the
‘b’ flag on platforms where that makes a difference. An optional <em>dialect</em>
parameter can be given which is used to define a set of parameters specific to a
particular CSV dialect. It may be an instance of a subclass of the
<a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class or one of the strings returned by the
<a class="reference internal" href="#csv.list_dialects" title="csv.list_dialects"><code class="xref py py-func docutils literal notranslate"><span class="pre">list_dialects()</span></code></a> function. The other optional <em>fmtparams</em> keyword arguments
can be given to override individual formatting parameters in the current
dialect. For full details about the dialect and formatting parameters, see
section <a class="reference internal" href="#csv-fmt-params"><span class="std std-ref">Dialects and Formatting Parameters</span></a>. To make it
as easy as possible to interface with modules which implement the DB API, the
value <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> is written as the empty string. While this isn’t a
reversible transformation, it makes it easier to dump SQL NULL data values to
CSV files without preprocessing the data returned from a <code class="docutils literal notranslate"><span class="pre">cursor.fetch*</span></code> call.
Floats are stringified with <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> before being written.
All other non-string data are stringified with <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a> before being written.</p>
<p>A short usage example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'eggs.csv'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">csvfile</span><span class="p">:</span>
<span class="n">spamwriter</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="n">csvfile</span><span class="p">,</span> <span class="n">delimiter</span><span class="o">=</span><span class="s1">' '</span><span class="p">,</span>
<span class="n">quotechar</span><span class="o">=</span><span class="s1">'|'</span><span class="p">,</span> <span class="n">quoting</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">QUOTE_MINIMAL</span><span class="p">)</span>
<span class="n">spamwriter</span><span class="o">.</span><span class="n">writerow</span><span class="p">([</span><span class="s1">'Spam'</span><span class="p">]</span> <span class="o">*</span> <span class="mi">5</span> <span class="o">+</span> <span class="p">[</span><span class="s1">'Baked Beans'</span><span class="p">])</span>
<span class="n">spamwriter</span><span class="o">.</span><span class="n">writerow</span><span class="p">([</span><span class="s1">'Spam'</span><span class="p">,</span> <span class="s1">'Lovely Spam'</span><span class="p">,</span> <span class="s1">'Wonderful Spam'</span><span class="p">])</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="csv.register_dialect">
<code class="descclassname">csv.</code><code class="descname">register_dialect</code><span class="sig-paren">(</span><em>name</em>, <span class="optional">[</span><em>dialect</em>, <span class="optional">]</span><em>**fmtparams</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.register_dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>Associate <em>dialect</em> with <em>name</em>. <em>name</em> must be a string or Unicode object. The
dialect can be specified either by passing a sub-class of <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a>, or
by <em>fmtparams</em> keyword arguments, or both, with keyword arguments overriding
parameters of the dialect. For full details about the dialect and formatting
parameters, see section <a class="reference internal" href="#csv-fmt-params"><span class="std std-ref">Dialects and Formatting Parameters</span></a>.</p>
</dd></dl>
<dl class="function">
<dt id="csv.unregister_dialect">
<code class="descclassname">csv.</code><code class="descname">unregister_dialect</code><span class="sig-paren">(</span><em>name</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.unregister_dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>Delete the dialect associated with <em>name</em> from the dialect registry. An
<a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Error</span></code></a> is raised if <em>name</em> is not a registered dialect name.</p>
</dd></dl>
<dl class="function">
<dt id="csv.get_dialect">
<code class="descclassname">csv.</code><code class="descname">get_dialect</code><span class="sig-paren">(</span><em>name</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.get_dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the dialect associated with <em>name</em>. An <a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Error</span></code></a> is raised if <em>name</em>
is not a registered dialect name.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.5: </span>This function now returns an immutable <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a>. Previously an
instance of the requested dialect was returned. Users could modify the
underlying class, changing the behavior of active readers and writers.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="csv.list_dialects">
<code class="descclassname">csv.</code><code class="descname">list_dialects</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#csv.list_dialects" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the names of all registered dialects.</p>
</dd></dl>
<dl class="function">
<dt id="csv.field_size_limit">
<code class="descclassname">csv.</code><code class="descname">field_size_limit</code><span class="sig-paren">(</span><span class="optional">[</span><em>new_limit</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#csv.field_size_limit" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns the current maximum field size allowed by the parser. If <em>new_limit</em> is
given, this becomes the new limit.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.5.</span></p>
</div>
</dd></dl>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module defines the following classes:</p>
<dl class="class">
<dt id="csv.DictReader">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">DictReader</code><span class="sig-paren">(</span><em>f</em>, <em>fieldnames=None</em>, <em>restkey=None</em>, <em>restval=None</em>, <em>dialect='excel'</em>, <em>*args</em>, <em>**kwds</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.DictReader" title="Permalink to this definition">¶</a></dt>
<dd><p>Create an object which operates like a regular reader but maps the
information read into a dict whose keys are given by the optional
<em>fieldnames</em> parameter. The <em>fieldnames</em> parameter is a <a class="reference internal" href="collections.html#collections-abstract-base-classes"><span class="std std-ref">sequence</span></a> whose elements are associated with the
fields of the input data in order. These elements become the keys of the
resulting dictionary. If the <em>fieldnames</em> parameter is omitted, the values
in the first row of the file <em>f</em> will be used as the fieldnames. If the
row read has more fields than the fieldnames sequence, the remaining data is
added as a sequence keyed by the value of <em>restkey</em>. If the row read has
fewer fields than the fieldnames sequence, the remaining keys take the value
of the optional <em>restval</em> parameter. Any other optional or keyword
arguments are passed to the underlying <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> instance.</p>
<p>A short usage example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">csv</span>
<span class="gp">>>> </span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'names.csv'</span><span class="p">)</span> <span class="k">as</span> <span class="n">csvfile</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">DictReader</span><span class="p">(</span><span class="n">csvfile</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">reader</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">row</span><span class="p">[</span><span class="s1">'first_name'</span><span class="p">],</span> <span class="n">row</span><span class="p">[</span><span class="s1">'last_name'</span><span class="p">])</span>
<span class="gp">...</span>
<span class="go">Baked Beans</span>
<span class="go">Lovely Spam</span>
<span class="go">Wonderful Spam</span>
</pre></div>
</div>
</dd></dl>
<dl class="class">
<dt id="csv.DictWriter">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">DictWriter</code><span class="sig-paren">(</span><em>f</em>, <em>fieldnames</em>, <em>restval=''</em>, <em>extrasaction='raise'</em>, <em>dialect='excel'</em>, <em>*args</em>, <em>**kwds</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.DictWriter" title="Permalink to this definition">¶</a></dt>
<dd><p>Create an object which operates like a regular writer but maps dictionaries
onto output rows. The <em>fieldnames</em> parameter is a <a class="reference internal" href="collections.html#collections-abstract-base-classes"><span class="std std-ref">sequence</span></a> of keys that identify the order in
which values in the dictionary passed to the <code class="xref py py-meth docutils literal notranslate"><span class="pre">writerow()</span></code> method are
written to the file <em>f</em>. The optional <em>restval</em> parameter specifies the
value to be written if the dictionary is missing a key in <em>fieldnames</em>. If
the dictionary passed to the <code class="xref py py-meth docutils literal notranslate"><span class="pre">writerow()</span></code> method contains a key not
found in <em>fieldnames</em>, the optional <em>extrasaction</em> parameter indicates what
action to take. If it is set to <code class="docutils literal notranslate"><span class="pre">'raise'</span></code> a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> is raised.
If it is set to <code class="docutils literal notranslate"><span class="pre">'ignore'</span></code>, extra values in the dictionary are ignored.
Any other optional or keyword arguments are passed to the underlying
<a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> instance.</p>
<p>Note that unlike the <a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictReader</span></code></a> class, the <em>fieldnames</em> parameter
of the <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictWriter</span></code></a> is not optional. Since Python’s <a class="reference internal" href="stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>
objects are not ordered, there is not enough information available to deduce
the order in which the row should be written to the file <em>f</em>.</p>
<p>A short usage example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'names.csv'</span><span class="p">,</span> <span class="s1">'w'</span><span class="p">)</span> <span class="k">as</span> <span class="n">csvfile</span><span class="p">:</span>
<span class="n">fieldnames</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'first_name'</span><span class="p">,</span> <span class="s1">'last_name'</span><span class="p">]</span>
<span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">DictWriter</span><span class="p">(</span><span class="n">csvfile</span><span class="p">,</span> <span class="n">fieldnames</span><span class="o">=</span><span class="n">fieldnames</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writeheader</span><span class="p">()</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">({</span><span class="s1">'first_name'</span><span class="p">:</span> <span class="s1">'Baked'</span><span class="p">,</span> <span class="s1">'last_name'</span><span class="p">:</span> <span class="s1">'Beans'</span><span class="p">})</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">({</span><span class="s1">'first_name'</span><span class="p">:</span> <span class="s1">'Lovely'</span><span class="p">,</span> <span class="s1">'last_name'</span><span class="p">:</span> <span class="s1">'Spam'</span><span class="p">})</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">({</span><span class="s1">'first_name'</span><span class="p">:</span> <span class="s1">'Wonderful'</span><span class="p">,</span> <span class="s1">'last_name'</span><span class="p">:</span> <span class="s1">'Spam'</span><span class="p">})</span>
</pre></div>
</div>
</dd></dl>
<dl class="class">
<dt id="csv.Dialect">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">Dialect</code><a class="headerlink" href="#csv.Dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class is a container class relied on primarily for its
attributes, which are used to define the parameters for a specific
<a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> or <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> instance.</p>
</dd></dl>
<dl class="class">
<dt id="csv.excel">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">excel</code><a class="headerlink" href="#csv.excel" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#csv.excel" title="csv.excel"><code class="xref py py-class docutils literal notranslate"><span class="pre">excel</span></code></a> class defines the usual properties of an Excel-generated CSV
file. It is registered with the dialect name <code class="docutils literal notranslate"><span class="pre">'excel'</span></code>.</p>
</dd></dl>
<dl class="class">
<dt id="csv.excel_tab">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">excel_tab</code><a class="headerlink" href="#csv.excel_tab" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#csv.excel_tab" title="csv.excel_tab"><code class="xref py py-class docutils literal notranslate"><span class="pre">excel_tab</span></code></a> class defines the usual properties of an Excel-generated
TAB-delimited file. It is registered with the dialect name <code class="docutils literal notranslate"><span class="pre">'excel-tab'</span></code>.</p>
</dd></dl>
<dl class="class">
<dt id="csv.Sniffer">
<em class="property">class </em><code class="descclassname">csv.</code><code class="descname">Sniffer</code><a class="headerlink" href="#csv.Sniffer" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate"><span class="pre">Sniffer</span></code></a> class is used to deduce the format of a CSV file.</p>
<p>The <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate"><span class="pre">Sniffer</span></code></a> class provides two methods:</p>
<dl class="method">
<dt id="csv.Sniffer.sniff">
<code class="descname">sniff</code><span class="sig-paren">(</span><em>sample</em>, <em>delimiters=None</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.Sniffer.sniff" title="Permalink to this definition">¶</a></dt>
<dd><p>Analyze the given <em>sample</em> and return a <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> subclass
reflecting the parameters found. If the optional <em>delimiters</em> parameter
is given, it is interpreted as a string containing possible valid
delimiter characters.</p>
</dd></dl>
<dl class="method">
<dt id="csv.Sniffer.has_header">
<code class="descname">has_header</code><span class="sig-paren">(</span><em>sample</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.Sniffer.has_header" title="Permalink to this definition">¶</a></dt>
<dd><p>Analyze the sample text (presumed to be in CSV format) and return
<a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a> if the first row appears to be a series of column headers.</p>
</dd></dl>
</dd></dl>
<p>An example for <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate"><span class="pre">Sniffer</span></code></a> use:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'example.csv'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">csvfile</span><span class="p">:</span>
<span class="n">dialect</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">Sniffer</span><span class="p">()</span><span class="o">.</span><span class="n">sniff</span><span class="p">(</span><span class="n">csvfile</span><span class="o">.</span><span class="n">read</span><span class="p">(</span><span class="mi">1024</span><span class="p">))</span>
<span class="n">csvfile</span><span class="o">.</span><span class="n">seek</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">csvfile</span><span class="p">,</span> <span class="n">dialect</span><span class="p">)</span>
<span class="c1"># ... process CSV file contents here ...</span>
</pre></div>
</div>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module defines the following constants:</p>
<dl class="data">
<dt id="csv.QUOTE_ALL">
<code class="descclassname">csv.</code><code class="descname">QUOTE_ALL</code><a class="headerlink" href="#csv.QUOTE_ALL" title="Permalink to this definition">¶</a></dt>
<dd><p>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects to quote all fields.</p>
</dd></dl>
<dl class="data">
<dt id="csv.QUOTE_MINIMAL">
<code class="descclassname">csv.</code><code class="descname">QUOTE_MINIMAL</code><a class="headerlink" href="#csv.QUOTE_MINIMAL" title="Permalink to this definition">¶</a></dt>
<dd><p>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects to only quote those fields which contain
special characters such as <em>delimiter</em>, <em>quotechar</em> or any of the characters in
<em>lineterminator</em>.</p>
</dd></dl>
<dl class="data">
<dt id="csv.QUOTE_NONNUMERIC">
<code class="descclassname">csv.</code><code class="descname">QUOTE_NONNUMERIC</code><a class="headerlink" href="#csv.QUOTE_NONNUMERIC" title="Permalink to this definition">¶</a></dt>
<dd><p>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects to quote all non-numeric fields.</p>
<p>Instructs the reader to convert all non-quoted fields to type <em>float</em>.</p>
</dd></dl>
<dl class="data">
<dt id="csv.QUOTE_NONE">
<code class="descclassname">csv.</code><code class="descname">QUOTE_NONE</code><a class="headerlink" href="#csv.QUOTE_NONE" title="Permalink to this definition">¶</a></dt>
<dd><p>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects to never quote fields. When the current
<em>delimiter</em> occurs in output data it is preceded by the current <em>escapechar</em>
character. If <em>escapechar</em> is not set, the writer will raise <a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Error</span></code></a> if
any characters that require escaping are encountered.</p>
<p>Instructs <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> to perform no special processing of quote characters.</p>
</dd></dl>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module defines the following exception:</p>
<dl class="exception">
<dt id="csv.Error">
<em class="property">exception </em><code class="descclassname">csv.</code><code class="descname">Error</code><a class="headerlink" href="#csv.Error" title="Permalink to this definition">¶</a></dt>
<dd><p>Raised by any of the functions when an error is detected.</p>
</dd></dl>
</div>
<div class="section" id="dialects-and-formatting-parameters">
<span id="csv-fmt-params"></span><h2>13.1.2. Dialects and Formatting Parameters<a class="headerlink" href="#dialects-and-formatting-parameters" title="Permalink to this headline">¶</a></h2>
<p>To make it easier to specify the format of input and output records, specific
formatting parameters are grouped together into dialects. A dialect is a
subclass of the <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class having a set of specific methods and a
single <code class="xref py py-meth docutils literal notranslate"><span class="pre">validate()</span></code> method. When creating <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> or
<a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a> objects, the programmer can specify a string or a subclass of
the <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class as the dialect parameter. In addition to, or instead
of, the <em>dialect</em> parameter, the programmer can also specify individual
formatting parameters, which have the same names as the attributes defined below
for the <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate"><span class="pre">Dialect</span></code></a> class.</p>
<p>Dialects support the following attributes:</p>
<dl class="attribute">
<dt id="csv.Dialect.delimiter">
<code class="descclassname">Dialect.</code><code class="descname">delimiter</code><a class="headerlink" href="#csv.Dialect.delimiter" title="Permalink to this definition">¶</a></dt>
<dd><p>A one-character string used to separate fields. It defaults to <code class="docutils literal notranslate"><span class="pre">','</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.doublequote">
<code class="descclassname">Dialect.</code><code class="descname">doublequote</code><a class="headerlink" href="#csv.Dialect.doublequote" title="Permalink to this definition">¶</a></dt>
<dd><p>Controls how instances of <em>quotechar</em> appearing inside a field should
themselves be quoted. When <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a>, the character is doubled. When
<a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a>, the <em>escapechar</em> is used as a prefix to the <em>quotechar</em>. It
defaults to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a>.</p>
<p>On output, if <em>doublequote</em> is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a> and no <em>escapechar</em> is set,
<a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Error</span></code></a> is raised if a <em>quotechar</em> is found in a field.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.escapechar">
<code class="descclassname">Dialect.</code><code class="descname">escapechar</code><a class="headerlink" href="#csv.Dialect.escapechar" title="Permalink to this definition">¶</a></dt>
<dd><p>A one-character string used by the writer to escape the <em>delimiter</em> if <em>quoting</em>
is set to <a class="reference internal" href="#csv.QUOTE_NONE" title="csv.QUOTE_NONE"><code class="xref py py-const docutils literal notranslate"><span class="pre">QUOTE_NONE</span></code></a> and the <em>quotechar</em> if <em>doublequote</em> is
<a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a>. On reading, the <em>escapechar</em> removes any special meaning from
the following character. It defaults to <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>, which disables escaping.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.lineterminator">
<code class="descclassname">Dialect.</code><code class="descname">lineterminator</code><a class="headerlink" href="#csv.Dialect.lineterminator" title="Permalink to this definition">¶</a></dt>
<dd><p>The string used to terminate lines produced by the <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate"><span class="pre">writer</span></code></a>. It defaults
to <code class="docutils literal notranslate"><span class="pre">'\r\n'</span></code>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">reader</span></code></a> is hard-coded to recognise either <code class="docutils literal notranslate"><span class="pre">'\r'</span></code> or <code class="docutils literal notranslate"><span class="pre">'\n'</span></code> as
end-of-line, and ignores <em>lineterminator</em>. This behavior may change in the
future.</p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.quotechar">
<code class="descclassname">Dialect.</code><code class="descname">quotechar</code><a class="headerlink" href="#csv.Dialect.quotechar" title="Permalink to this definition">¶</a></dt>
<dd><p>A one-character string used to quote fields containing special characters, such
as the <em>delimiter</em> or <em>quotechar</em>, or which contain new-line characters. It
defaults to <code class="docutils literal notranslate"><span class="pre">'"'</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.quoting">
<code class="descclassname">Dialect.</code><code class="descname">quoting</code><a class="headerlink" href="#csv.Dialect.quoting" title="Permalink to this definition">¶</a></dt>
<dd><p>Controls when quotes should be generated by the writer and recognised by the
reader. It can take on any of the <code class="xref py py-const docutils literal notranslate"><span class="pre">QUOTE_*</span></code> constants (see section
<a class="reference internal" href="#csv-contents"><span class="std std-ref">Module Contents</span></a>) and defaults to <a class="reference internal" href="#csv.QUOTE_MINIMAL" title="csv.QUOTE_MINIMAL"><code class="xref py py-const docutils literal notranslate"><span class="pre">QUOTE_MINIMAL</span></code></a>.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.skipinitialspace">
<code class="descclassname">Dialect.</code><code class="descname">skipinitialspace</code><a class="headerlink" href="#csv.Dialect.skipinitialspace" title="Permalink to this definition">¶</a></dt>
<dd><p>When <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a>, whitespace immediately following the <em>delimiter</em> is ignored.
The default is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a>.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.Dialect.strict">
<code class="descclassname">Dialect.</code><code class="descname">strict</code><a class="headerlink" href="#csv.Dialect.strict" title="Permalink to this definition">¶</a></dt>
<dd><p>When <code class="docutils literal notranslate"><span class="pre">True</span></code>, raise exception <a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Error</span></code></a> on bad CSV input.
The default is <code class="docutils literal notranslate"><span class="pre">False</span></code>.</p>
</dd></dl>
</div>
<div class="section" id="reader-objects">
<h2>13.1.3. Reader Objects<a class="headerlink" href="#reader-objects" title="Permalink to this headline">¶</a></h2>
<p>Reader objects (<a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictReader</span></code></a> instances and objects returned by the
<a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-func docutils literal notranslate"><span class="pre">reader()</span></code></a> function) have the following public methods:</p>
<dl class="method">
<dt id="csv.csvreader.next">
<code class="descclassname">csvreader.</code><code class="descname">next</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#csv.csvreader.next" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the next row of the reader’s iterable object as a list, parsed according
to the current dialect.</p>
</dd></dl>
<p>Reader objects have the following public attributes:</p>
<dl class="attribute">
<dt id="csv.csvreader.dialect">
<code class="descclassname">csvreader.</code><code class="descname">dialect</code><a class="headerlink" href="#csv.csvreader.dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>A read-only description of the dialect in use by the parser.</p>
</dd></dl>
<dl class="attribute">
<dt id="csv.csvreader.line_num">
<code class="descclassname">csvreader.</code><code class="descname">line_num</code><a class="headerlink" href="#csv.csvreader.line_num" title="Permalink to this definition">¶</a></dt>
<dd><p>The number of lines read from the source iterator. This is not the same as the
number of records returned, as records can span multiple lines.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.5.</span></p>
</div>
</dd></dl>
<p>DictReader objects have the following public attribute:</p>
<dl class="attribute">
<dt id="csv.csvreader.fieldnames">
<code class="descclassname">csvreader.</code><code class="descname">fieldnames</code><a class="headerlink" href="#csv.csvreader.fieldnames" title="Permalink to this definition">¶</a></dt>
<dd><p>If not passed as a parameter when creating the object, this attribute is
initialized upon first access or when the first record is read from the
file.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.6.</span></p>
</div>
</dd></dl>
</div>
<div class="section" id="writer-objects">
<h2>13.1.4. Writer Objects<a class="headerlink" href="#writer-objects" title="Permalink to this headline">¶</a></h2>
<p><code class="xref py py-class docutils literal notranslate"><span class="pre">Writer</span></code> objects (<a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictWriter</span></code></a> instances and objects returned by
the <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-func docutils literal notranslate"><span class="pre">writer()</span></code></a> function) have the following public methods. A <em>row</em> must be
a sequence of strings or numbers for <code class="xref py py-class docutils literal notranslate"><span class="pre">Writer</span></code> objects and a dictionary
mapping fieldnames to strings or numbers (by passing them through <a class="reference internal" href="functions.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a>
first) for <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate"><span class="pre">DictWriter</span></code></a> objects. Note that complex numbers are written
out surrounded by parens. This may cause some problems for other programs which
read CSV files (assuming they support complex numbers at all).</p>
<dl class="method">
<dt id="csv.csvwriter.writerow">
<code class="descclassname">csvwriter.</code><code class="descname">writerow</code><span class="sig-paren">(</span><em>row</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.csvwriter.writerow" title="Permalink to this definition">¶</a></dt>
<dd><p>Write the <em>row</em> parameter to the writer’s file object, formatted according to
the current dialect.</p>
</dd></dl>
<dl class="method">
<dt id="csv.csvwriter.writerows">
<code class="descclassname">csvwriter.</code><code class="descname">writerows</code><span class="sig-paren">(</span><em>rows</em><span class="sig-paren">)</span><a class="headerlink" href="#csv.csvwriter.writerows" title="Permalink to this definition">¶</a></dt>
<dd><p>Write all elements in <em>rows</em> (an iterable of <em>row</em> objects as described
above) to the writer’s file object, formatted according to the current
dialect.</p>
</dd></dl>
<p>Writer objects have the following public attribute:</p>
<dl class="attribute">
<dt id="csv.csvwriter.dialect">
<code class="descclassname">csvwriter.</code><code class="descname">dialect</code><a class="headerlink" href="#csv.csvwriter.dialect" title="Permalink to this definition">¶</a></dt>
<dd><p>A read-only description of the dialect in use by the writer.</p>
</dd></dl>
<p>DictWriter objects have the following public method:</p>
<dl class="method">
<dt id="csv.DictWriter.writeheader">
<code class="descclassname">DictWriter.</code><code class="descname">writeheader</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#csv.DictWriter.writeheader" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a row with the field names (as specified in the constructor).</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.7.</span></p>
</div>
</dd></dl>
</div>
<div class="section" id="examples">
<span id="csv-examples"></span><h2>13.1.5. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<p>The simplest example of reading a CSV file:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'some.csv'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">reader</span><span class="p">:</span>
<span class="nb">print</span> <span class="n">row</span>
</pre></div>
</div>
<p>Reading a file with an alternate format:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'passwd'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">delimiter</span><span class="o">=</span><span class="s1">':'</span><span class="p">,</span> <span class="n">quoting</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">QUOTE_NONE</span><span class="p">)</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">reader</span><span class="p">:</span>
<span class="nb">print</span> <span class="n">row</span>
</pre></div>
</div>
<p>The corresponding simplest possible writing example is:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'some.csv'</span><span class="p">,</span> <span class="s1">'wb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">writerows</span><span class="p">(</span><span class="n">someiterable</span><span class="p">)</span>
</pre></div>
</div>
<p>Registering a new dialect:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="n">csv</span><span class="o">.</span><span class="n">register_dialect</span><span class="p">(</span><span class="s1">'unixpwd'</span><span class="p">,</span> <span class="n">delimiter</span><span class="o">=</span><span class="s1">':'</span><span class="p">,</span> <span class="n">quoting</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">QUOTE_NONE</span><span class="p">)</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">'passwd'</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="s1">'unixpwd'</span><span class="p">)</span>
</pre></div>
</div>
<p>A slightly more advanced use of the reader — catching and reporting errors:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span><span class="o">,</span> <span class="nn">sys</span>
<span class="n">filename</span> <span class="o">=</span> <span class="s1">'some.csv'</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">,</span> <span class="s1">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">reader</span><span class="p">:</span>
<span class="nb">print</span> <span class="n">row</span>
<span class="k">except</span> <span class="n">csv</span><span class="o">.</span><span class="n">Error</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="s1">'file </span><span class="si">%s</span><span class="s1">, line </span><span class="si">%d</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">filename</span><span class="p">,</span> <span class="n">reader</span><span class="o">.</span><span class="n">line_num</span><span class="p">,</span> <span class="n">e</span><span class="p">))</span>
</pre></div>
</div>
<p>And while the module doesn’t directly support parsing strings, it can easily be
done:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">([</span><span class="s1">'one,two,three'</span><span class="p">]):</span>
<span class="nb">print</span> <span class="n">row</span>
</pre></div>
</div>
<p>The <a class="reference internal" href="#module-csv" title="csv: Write and read tabular data to and from delimited files."><code class="xref py py-mod docutils literal notranslate"><span class="pre">csv</span></code></a> module doesn’t directly support reading and writing Unicode, but
it is 8-bit-clean save for some problems with ASCII NUL characters. So you can
write functions or classes that handle the encoding and decoding for you as long
as you avoid encodings like UTF-16 that use NULs. UTF-8 is recommended.</p>
<p><code class="xref py py-func docutils literal notranslate"><span class="pre">unicode_csv_reader()</span></code> below is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a> that wraps <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate"><span class="pre">csv.reader</span></code></a>
to handle Unicode CSV data (a list of Unicode strings). <code class="xref py py-func docutils literal notranslate"><span class="pre">utf_8_encoder()</span></code>
is a <a class="reference internal" href="../glossary.html#term-generator"><span class="xref std std-term">generator</span></a> that encodes the Unicode strings as UTF-8, one string (or row) at
a time. The encoded strings are parsed by the CSV reader, and
<code class="xref py py-func docutils literal notranslate"><span class="pre">unicode_csv_reader()</span></code> decodes the UTF-8-encoded cells back into Unicode:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span>
<span class="k">def</span> <span class="nf">unicode_csv_reader</span><span class="p">(</span><span class="n">unicode_csv_data</span><span class="p">,</span> <span class="n">dialect</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">excel</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="c1"># csv.py doesn't do Unicode; encode temporarily as UTF-8:</span>
<span class="n">csv_reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">utf_8_encoder</span><span class="p">(</span><span class="n">unicode_csv_data</span><span class="p">),</span>
<span class="n">dialect</span><span class="o">=</span><span class="n">dialect</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">csv_reader</span><span class="p">:</span>
<span class="c1"># decode UTF-8 back to Unicode, cell by cell:</span>
<span class="k">yield</span> <span class="p">[</span><span class="n">unicode</span><span class="p">(</span><span class="n">cell</span><span class="p">,</span> <span class="s1">'utf-8'</span><span class="p">)</span> <span class="k">for</span> <span class="n">cell</span> <span class="ow">in</span> <span class="n">row</span><span class="p">]</span>
<span class="k">def</span> <span class="nf">utf_8_encoder</span><span class="p">(</span><span class="n">unicode_csv_data</span><span class="p">):</span>
<span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">unicode_csv_data</span><span class="p">:</span>
<span class="k">yield</span> <span class="n">line</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'utf-8'</span><span class="p">)</span>
</pre></div>
</div>
<p>For all other encodings the following <code class="xref py py-class docutils literal notranslate"><span class="pre">UnicodeReader</span></code> and
<code class="xref py py-class docutils literal notranslate"><span class="pre">UnicodeWriter</span></code> classes can be used. They take an additional <em>encoding</em>
parameter in their constructor and make sure that the data passes the real
reader or writer encoded as UTF-8:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">csv</span><span class="o">,</span> <span class="nn">codecs</span><span class="o">,</span> <span class="nn">cStringIO</span>
<span class="k">class</span> <span class="nc">UTF8Recoder</span><span class="p">:</span>
<span class="sd">"""</span>
<span class="sd"> Iterator that reads an encoded stream and reencodes the input to UTF-8</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">f</span><span class="p">,</span> <span class="n">encoding</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reader</span> <span class="o">=</span> <span class="n">codecs</span><span class="o">.</span><span class="n">getreader</span><span class="p">(</span><span class="n">encoding</span><span class="p">)(</span><span class="n">f</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span>
<span class="k">def</span> <span class="nf">next</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">reader</span><span class="o">.</span><span class="n">next</span><span class="p">()</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s2">"utf-8"</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">UnicodeReader</span><span class="p">:</span>
<span class="sd">"""</span>
<span class="sd"> A CSV reader which will iterate over lines in the CSV file "f",</span>
<span class="sd"> which is encoded in the given encoding.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">f</span><span class="p">,</span> <span class="n">dialect</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">excel</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s2">"utf-8"</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">UTF8Recoder</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">encoding</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reader</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">dialect</span><span class="o">=</span><span class="n">dialect</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">next</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">row</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">reader</span><span class="o">.</span><span class="n">next</span><span class="p">()</span>
<span class="k">return</span> <span class="p">[</span><span class="n">unicode</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="s2">"utf-8"</span><span class="p">)</span> <span class="k">for</span> <span class="n">s</span> <span class="ow">in</span> <span class="n">row</span><span class="p">]</span>
<span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span>
<span class="k">class</span> <span class="nc">UnicodeWriter</span><span class="p">:</span>
<span class="sd">"""</span>
<span class="sd"> A CSV writer which will write rows to CSV file "f",</span>
<span class="sd"> which is encoded in the given encoding.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">f</span><span class="p">,</span> <span class="n">dialect</span><span class="o">=</span><span class="n">csv</span><span class="o">.</span><span class="n">excel</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s2">"utf-8"</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span>
<span class="c1"># Redirect output to a queue</span>
<span class="bp">self</span><span class="o">.</span><span class="n">queue</span> <span class="o">=</span> <span class="n">cStringIO</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span>
<span class="bp">self</span><span class="o">.</span><span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="p">,</span> <span class="n">dialect</span><span class="o">=</span><span class="n">dialect</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">stream</span> <span class="o">=</span> <span class="n">f</span>
<span class="bp">self</span><span class="o">.</span><span class="n">encoder</span> <span class="o">=</span> <span class="n">codecs</span><span class="o">.</span><span class="n">getincrementalencoder</span><span class="p">(</span><span class="n">encoding</span><span class="p">)()</span>
<span class="k">def</span> <span class="nf">writerow</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">row</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">([</span><span class="n">s</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s2">"utf-8"</span><span class="p">)</span> <span class="k">for</span> <span class="n">s</span> <span class="ow">in</span> <span class="n">row</span><span class="p">])</span>
<span class="c1"># Fetch UTF-8 output from the queue ...</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s2">"utf-8"</span><span class="p">)</span>
<span class="c1"># ... and reencode it into the target encoding</span>
<span class="n">data</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">encoder</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="c1"># write to the target stream</span>
<span class="bp">self</span><span class="o">.</span><span class="n">stream</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="c1"># empty queue</span>
<span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">truncate</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">writerows</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">rows</span><span class="p">):</span>
<span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">rows</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">writerow</span><span class="p">(</span><span class="n">row</span><span class="p">)</span>
</pre></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="#">13.1. <code class="docutils literal notranslate"><span class="pre">csv</span></code> — CSV File Reading and Writing</a><ul>
<li><a class="reference internal" href="#module-contents">13.1.1. Module Contents</a></li>
<li><a class="reference internal" href="#dialects-and-formatting-parameters">13.1.2. Dialects and Formatting Parameters</a></li>
<li><a class="reference internal" href="#reader-objects">13.1.3. Reader Objects</a></li>
<li><a class="reference internal" href="#writer-objects">13.1.4. Writer Objects</a></li>
<li><a class="reference internal" href="#examples">13.1.5. Examples</a></li>
</ul>
</li>
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title="previous chapter">13. File Formats</a></p>
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<p class="topless"><a href="configparser.html"
title="next chapter">13.2. <code class="docutils literal notranslate"><span class="pre">ConfigParser</span></code> — Configuration file parser</a></p>
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