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 <section id="module-csv">
<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">csv</code></a> — CSV File Reading and Writing<a class="headerlink" href="#module-csv" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 2.3.
</div>
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.
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">csv</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.
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">csv</code></a> module’s <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate">reader</code></a> and <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</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">DictReader</code></a> and <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate">DictWriter</code></a> classes.
<div class="admonition note">
Note
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">csv</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">Examples</a>.
</div>
<div class="admonition seealso">
See also
<dl class="simple">
<dt><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0305">PEP 305</a> - CSV File API</dt><dd>The Python Enhancement Proposal which proposed this addition to Python.
</dd>
</dl>
</div>
<section id="module-contents">
<h2>13.1.1. Module Contents<a class="headerlink" href="#module-contents" title="Permalink to this headline">¶</a></h2>
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">csv</code></a> module defines the following functions:
<dl class="py function">
<dt class="sig sig-object py" id="csv.reader">
csv.reader(csvfile, dialect='excel', **fmtparams)<a class="headerlink" href="#csv.reader" title="Permalink to this definition">¶</a></dt>
<dd>Return a reader object which will iterate over lines in the given csvfile.
csvfile can be any object which supports the <a class="reference internal" href="../glossary.html#term-iterator">iterator</a> protocol and returns a
string each time its <code class="xref py py-meth docutils literal notranslate">next()</code> method is called — file objects and list
objects are both suitable. If csvfile is a file object, it must be opened
with the ‘b’ flag on platforms where that makes a difference. An optional
dialect 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">Dialect</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">list_dialects()</code></a> function. The other optional fmtparams 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">Dialects and Formatting Parameters</a>.
Each row read from the csv file is returned as a list of strings. No
automatic data type conversion is performed.
A short usage example:
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import csv
&gt;&gt;&gt; with open(&#39;eggs.csv&#39;, &#39;rb&#39;) as csvfile:
... spamreader = csv.reader(csvfile, delimiter=&#39; &#39;, quotechar=&#39;|&#39;)
... for row in spamreader:
... print &#39;, &#39;.join(row)
Spam, Spam, Spam, Spam, Spam, Baked Beans
Spam, Lovely Spam, Wonderful Spam
</pre></div>
</div>
<div class="versionchanged">
Changed in version 2.5: 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.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.writer">
csv.writer(csvfile, dialect='excel', **fmtparams)<a class="headerlink" href="#csv.writer" title="Permalink to this definition">¶</a></dt>
<dd>Return a writer object responsible for converting the user’s data into delimited
strings on the given file-like object. csvfile can be any object with a
<code class="xref py py-func docutils literal notranslate">write()</code> method. If csvfile is a file object, it must be opened with the
‘b’ flag on platforms where that makes a difference. An optional dialect
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">Dialect</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">list_dialects()</code></a> function. The other optional fmtparams 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">Dialects and Formatting Parameters</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">None</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">cursor.fetch*</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">repr()</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">str()</code></a> before being written.
A short usage example:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
with open(&#39;eggs.csv&#39;, &#39;wb&#39;) as csvfile:
 spamwriter = csv.writer(csvfile, delimiter=&#39; &#39;,
 quotechar=&#39;|&#39;, quoting=csv.QUOTE_MINIMAL)
 spamwriter.writerow([&#39;Spam&#39;] * 5 + [&#39;Baked Beans&#39;])
 spamwriter.writerow([&#39;Spam&#39;, &#39;Lovely Spam&#39;, &#39;Wonderful Spam&#39;])
</pre></div>
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.register_dialect">
csv.register_dialect(name, [dialect, ]**fmtparams)<a class="headerlink" href="#csv.register_dialect" title="Permalink to this definition">¶</a></dt>
<dd>Associate dialect with name. name 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">Dialect</code></a>, or
by fmtparams 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">Dialects and Formatting Parameters</a>.
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.unregister_dialect">
csv.unregister_dialect(name)<a class="headerlink" href="#csv.unregister_dialect" title="Permalink to this definition">¶</a></dt>
<dd>Delete the dialect associated with name from the dialect registry. An
<a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate">Error</code></a> is raised if name is not a registered dialect name.
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.get_dialect">
csv.get_dialect(name)<a class="headerlink" href="#csv.get_dialect" title="Permalink to this definition">¶</a></dt>
<dd>Return the dialect associated with name. An <a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate">Error</code></a> is raised if name
is not a registered dialect name.
<div class="versionchanged">
Changed in version 2.5: 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">Dialect</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.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.list_dialects">
csv.list_dialects()<a class="headerlink" href="#csv.list_dialects" title="Permalink to this definition">¶</a></dt>
<dd>Return the names of all registered dialects.
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="csv.field_size_limit">
csv.field_size_limit([new_limit])<a class="headerlink" href="#csv.field_size_limit" title="Permalink to this definition">¶</a></dt>
<dd>Returns the current maximum field size allowed by the parser. If new_limit is
given, this becomes the new limit.
<div class="versionadded">
New in version 2.5.
</div>
</dd></dl>

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">csv</code></a> module defines the following classes:
<dl class="py class">
<dt class="sig sig-object py" id="csv.DictReader">
class csv.DictReader(f, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)<a class="headerlink" href="#csv.DictReader" title="Permalink to this definition">¶</a></dt>
<dd>Create an object which operates like a regular reader but maps the
information read into a dict whose keys are given by the optional
fieldnames parameter. The fieldnames parameter is a <a class="reference internal" href="collections.html#collections-abstract-base-classes">sequence</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 fieldnames parameter is omitted, the values
in the first row of the file f 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 restkey. If the row read has
fewer fields than the fieldnames sequence, the remaining keys take the value
of the optional restval 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">reader</code></a> instance.
A short usage example:
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import csv
&gt;&gt;&gt; with open(&#39;names.csv&#39;) as csvfile:
... reader = csv.DictReader(csvfile)
... for row in reader:
... print(row[&#39;first_name&#39;], row[&#39;last_name&#39;])
...
Baked Beans
Lovely Spam
Wonderful Spam
</pre></div>
</div>
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="csv.DictWriter">
class csv.DictWriter(f, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)<a class="headerlink" href="#csv.DictWriter" title="Permalink to this definition">¶</a></dt>
<dd>Create an object which operates like a regular writer but maps dictionaries
onto output rows. The fieldnames parameter is a <a class="reference internal" href="collections.html#collections-abstract-base-classes">sequence</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">writerow()</code> method are
written to the file f. The optional restval parameter specifies the
value to be written if the dictionary is missing a key in fieldnames. If
the dictionary passed to the <code class="xref py py-meth docutils literal notranslate">writerow()</code> method contains a key not
found in fieldnames, the optional extrasaction parameter indicates what
action to take. If it is set to <code class="docutils literal notranslate">'raise'</code> a <code class="xref py py-exc docutils literal notranslate">ValueError</code> is raised.
If it is set to <code class="docutils literal notranslate">'ignore'</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">writer</code></a> instance.
Note that unlike the <a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate">DictReader</code></a> class, the fieldnames parameter
of the <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate">DictWriter</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">dict</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 f.
A short usage example:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv

with open(&#39;names.csv&#39;, &#39;w&#39;) as csvfile:
 fieldnames = [&#39;first_name&#39;, &#39;last_name&#39;]
 writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

writer.writeheader()
 writer.writerow({&#39;first_name&#39;: &#39;Baked&#39;, &#39;last_name&#39;: &#39;Beans&#39;})
 writer.writerow({&#39;first_name&#39;: &#39;Lovely&#39;, &#39;last_name&#39;: &#39;Spam&#39;})
 writer.writerow({&#39;first_name&#39;: &#39;Wonderful&#39;, &#39;last_name&#39;: &#39;Spam&#39;})
</pre></div>
</div>
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="csv.Dialect">
class csv.Dialect<a class="headerlink" href="#csv.Dialect" title="Permalink to this definition">¶</a></dt>
<dd>The <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate">Dialect</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">reader</code></a> or <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</code></a> instance.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="csv.excel">
class csv.excel<a class="headerlink" href="#csv.excel" title="Permalink to this definition">¶</a></dt>
<dd>The <a class="reference internal" href="#csv.excel" title="csv.excel"><code class="xref py py-class docutils literal notranslate">excel</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">'excel'</code>.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="csv.excel_tab">
class csv.excel_tab<a class="headerlink" href="#csv.excel_tab" title="Permalink to this definition">¶</a></dt>
<dd>The <a class="reference internal" href="#csv.excel_tab" title="csv.excel_tab"><code class="xref py py-class docutils literal notranslate">excel_tab</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">'excel-tab'</code>.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="csv.Sniffer">
class csv.Sniffer<a class="headerlink" href="#csv.Sniffer" title="Permalink to this definition">¶</a></dt>
<dd>The <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate">Sniffer</code></a> class is used to deduce the format of a CSV file.
The <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate">Sniffer</code></a> class provides two methods:
<dl class="py method">
<dt class="sig sig-object py" id="csv.Sniffer.sniff">
sniff(sample, delimiters=None)<a class="headerlink" href="#csv.Sniffer.sniff" title="Permalink to this definition">¶</a></dt>
<dd>Analyze the given sample and return a <a class="reference internal" href="#csv.Dialect" title="csv.Dialect"><code class="xref py py-class docutils literal notranslate">Dialect</code></a> subclass
reflecting the parameters found. If the optional delimiters parameter
is given, it is interpreted as a string containing possible valid
delimiter characters.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="csv.Sniffer.has_header">
has_header(sample)<a class="headerlink" href="#csv.Sniffer.has_header" title="Permalink to this definition">¶</a></dt>
<dd>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">True</code></a> if the first row appears to be a series of column headers.
</dd></dl>

</dd></dl>

An example for <a class="reference internal" href="#csv.Sniffer" title="csv.Sniffer"><code class="xref py py-class docutils literal notranslate">Sniffer</code></a> use:
<div class="highlight-default notranslate"><div class="highlight"><pre>with open(&#39;example.csv&#39;, &#39;rb&#39;) as csvfile:
 dialect = csv.Sniffer().sniff(csvfile.read(1024))
 csvfile.seek(0)
 reader = csv.reader(csvfile, dialect)
 # ... process CSV file contents here ...
</pre></div>
</div>
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">csv</code></a> module defines the following constants:
<dl class="py data">
<dt class="sig sig-object py" id="csv.QUOTE_ALL">
csv.QUOTE_ALL<a class="headerlink" href="#csv.QUOTE_ALL" title="Permalink to this definition">¶</a></dt>
<dd>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</code></a> objects to quote all fields.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="csv.QUOTE_MINIMAL">
csv.QUOTE_MINIMAL<a class="headerlink" href="#csv.QUOTE_MINIMAL" title="Permalink to this definition">¶</a></dt>
<dd>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</code></a> objects to only quote those fields which contain
special characters such as delimiter, quotechar or any of the characters in
lineterminator.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="csv.QUOTE_NONNUMERIC">
csv.QUOTE_NONNUMERIC<a class="headerlink" href="#csv.QUOTE_NONNUMERIC" title="Permalink to this definition">¶</a></dt>
<dd>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</code></a> objects to quote all non-numeric fields.
Instructs the reader to convert all non-quoted fields to type float.
</dd></dl>

<dl class="py data">
<dt class="sig sig-object py" id="csv.QUOTE_NONE">
csv.QUOTE_NONE<a class="headerlink" href="#csv.QUOTE_NONE" title="Permalink to this definition">¶</a></dt>
<dd>Instructs <a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</code></a> objects to never quote fields. When the current
delimiter occurs in output data it is preceded by the current escapechar
character. If escapechar 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">Error</code></a> if
any characters that require escaping are encountered.
Instructs <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate">reader</code></a> to perform no special processing of quote characters.
</dd></dl>

</section>
<section id="dialects-and-formatting-parameters">
<h2>13.1.2. Dialects and Formatting Parameters<a class="headerlink" href="#dialects-and-formatting-parameters" title="Permalink to this headline">¶</a></h2>
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">Dialect</code></a> class having a set of specific methods and a
single <code class="xref py py-meth docutils literal notranslate">validate()</code> method. When creating <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate">reader</code></a> or
<a class="reference internal" href="#csv.writer" title="csv.writer"><code class="xref py py-class docutils literal notranslate">writer</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">Dialect</code></a> class as the dialect parameter. In addition to, or instead
of, the dialect 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">Dialect</code></a> class.
Dialects support the following attributes:
<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.delimiter">
Dialect.delimiter<a class="headerlink" href="#csv.Dialect.delimiter" title="Permalink to this definition">¶</a></dt>
<dd>A one-character string used to separate fields. It defaults to <code class="docutils literal notranslate">','</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.doublequote">
Dialect.doublequote<a class="headerlink" href="#csv.Dialect.doublequote" title="Permalink to this definition">¶</a></dt>
<dd>Controls how instances of quotechar 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">True</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">False</code></a>, the escapechar is used as a prefix to the quotechar. It
defaults to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>.
On output, if doublequote is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a> and no escapechar is set,
<a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate">Error</code></a> is raised if a quotechar is found in a field.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.escapechar">
Dialect.escapechar<a class="headerlink" href="#csv.Dialect.escapechar" title="Permalink to this definition">¶</a></dt>
<dd>A one-character string used by the writer to escape the delimiter if quoting
is set to <a class="reference internal" href="#csv.QUOTE_NONE" title="csv.QUOTE_NONE"><code class="xref py py-const docutils literal notranslate">QUOTE_NONE</code></a> and the quotechar if doublequote is
<a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a>. On reading, the escapechar 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">None</code></a>, which disables escaping.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.lineterminator">
Dialect.lineterminator<a class="headerlink" href="#csv.Dialect.lineterminator" title="Permalink to this definition">¶</a></dt>
<dd>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">writer</code></a>. It defaults
to <code class="docutils literal notranslate">'\r\n'</code>.
<div class="admonition note">
Note
The <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate">reader</code></a> is hard-coded to recognise either <code class="docutils literal notranslate">'\r'</code> or <code class="docutils literal notranslate">'\n'</code> as
end-of-line, and ignores lineterminator. This behavior may change in the
future.
</div>
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.quotechar">
Dialect.quotechar<a class="headerlink" href="#csv.Dialect.quotechar" title="Permalink to this definition">¶</a></dt>
<dd>A one-character string used to quote fields containing special characters, such
as the delimiter or quotechar, or which contain new-line characters. It
defaults to <code class="docutils literal notranslate">'&quot;'</code>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.quoting">
Dialect.quoting<a class="headerlink" href="#csv.Dialect.quoting" title="Permalink to this definition">¶</a></dt>
<dd>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">QUOTE_*</code> constants (see section
<a class="reference internal" href="#csv-contents">Module Contents</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">QUOTE_MINIMAL</code></a>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.skipinitialspace">
Dialect.skipinitialspace<a class="headerlink" href="#csv.Dialect.skipinitialspace" title="Permalink to this definition">¶</a></dt>
<dd>When <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>, whitespace immediately following the delimiter is ignored.
The default is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a>.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.Dialect.strict">
Dialect.strict<a class="headerlink" href="#csv.Dialect.strict" title="Permalink to this definition">¶</a></dt>
<dd>When <code class="docutils literal notranslate">True</code>, raise exception <a class="reference internal" href="#csv.Error" title="csv.Error"><code class="xref py py-exc docutils literal notranslate">Error</code></a> on bad CSV input.
The default is <code class="docutils literal notranslate">False</code>.
</dd></dl>

</section>
<section id="reader-objects">
<h2>13.1.3. Reader Objects<a class="headerlink" href="#reader-objects" title="Permalink to this headline">¶</a></h2>
Reader objects (<a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate">DictReader</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">reader()</code></a> function) have the following public methods:
<dl class="py method">
<dt class="sig sig-object py" id="csv.csvreader.next">
csvreader.next()<a class="headerlink" href="#csv.csvreader.next" title="Permalink to this definition">¶</a></dt>
<dd>Return the next row of the reader’s iterable object as a list, parsed according
to the current dialect.
</dd></dl>

Reader objects have the following public attributes:
<dl class="py attribute">
<dt class="sig sig-object py" id="csv.csvreader.dialect">
csvreader.dialect<a class="headerlink" href="#csv.csvreader.dialect" title="Permalink to this definition">¶</a></dt>
<dd>A read-only description of the dialect in use by the parser.
</dd></dl>

<dl class="py attribute">
<dt class="sig sig-object py" id="csv.csvreader.line_num">
csvreader.line_num<a class="headerlink" href="#csv.csvreader.line_num" title="Permalink to this definition">¶</a></dt>
<dd>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.
<div class="versionadded">
New in version 2.5.
</div>
</dd></dl>

DictReader objects have the following public attribute:
<dl class="py attribute">
<dt class="sig sig-object py" id="csv.csvreader.fieldnames">
csvreader.fieldnames<a class="headerlink" href="#csv.csvreader.fieldnames" title="Permalink to this definition">¶</a></dt>
<dd>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.
<div class="versionchanged">
Changed in version 2.6.
</div>
</dd></dl>

</section>
<section id="writer-objects">
<h2>13.1.4. Writer Objects<a class="headerlink" href="#writer-objects" title="Permalink to this headline">¶</a></h2>
<code class="xref py py-class docutils literal notranslate">Writer</code> objects (<a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate">DictWriter</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">writer()</code></a> function) have the following public methods. A row must be
a sequence of strings or numbers for <code class="xref py py-class docutils literal notranslate">Writer</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">str()</code></a>
first) for <a class="reference internal" href="#csv.DictWriter" title="csv.DictWriter"><code class="xref py py-class docutils literal notranslate">DictWriter</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).
<dl class="py method">
<dt class="sig sig-object py" id="csv.csvwriter.writerow">
csvwriter.writerow(row)<a class="headerlink" href="#csv.csvwriter.writerow" title="Permalink to this definition">¶</a></dt>
<dd>Write the row parameter to the writer’s file object, formatted according to
the current dialect.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="csv.csvwriter.writerows">
csvwriter.writerows(rows)<a class="headerlink" href="#csv.csvwriter.writerows" title="Permalink to this definition">¶</a></dt>
<dd>Write all elements in rows (an iterable of row objects as described
above) to the writer’s file object, formatted according to the current
dialect.
</dd></dl>

Writer objects have the following public attribute:
<dl class="py attribute">
<dt class="sig sig-object py" id="csv.csvwriter.dialect">
csvwriter.dialect<a class="headerlink" href="#csv.csvwriter.dialect" title="Permalink to this definition">¶</a></dt>
<dd>A read-only description of the dialect in use by the writer.
</dd></dl>

DictWriter objects have the following public method:
<dl class="py method">
<dt class="sig sig-object py" id="csv.DictWriter.writeheader">
DictWriter.writeheader()<a class="headerlink" href="#csv.DictWriter.writeheader" title="Permalink to this definition">¶</a></dt>
<dd>Write a row with the field names (as specified in the constructor).
<div class="versionadded">
New in version 2.7.
</div>
</dd></dl>

</section>
<section id="examples">
<h2>13.1.5. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
The simplest example of reading a CSV file:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
with open(&#39;some.csv&#39;, &#39;rb&#39;) as f:
 reader = csv.reader(f)
 for row in reader:
 print row
</pre></div>
</div>
Reading a file with an alternate format:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
with open(&#39;passwd&#39;, &#39;rb&#39;) as f:
 reader = csv.reader(f, delimiter=&#39;:&#39;, quoting=csv.QUOTE_NONE)
 for row in reader:
 print row
</pre></div>
</div>
The corresponding simplest possible writing example is:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
with open(&#39;some.csv&#39;, &#39;wb&#39;) as f:
 writer = csv.writer(f)
 writer.writerows(someiterable)
</pre></div>
</div>
Registering a new dialect:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
csv.register_dialect(&#39;unixpwd&#39;, delimiter=&#39;:&#39;, quoting=csv.QUOTE_NONE)
with open(&#39;passwd&#39;, &#39;rb&#39;) as f:
 reader = csv.reader(f, &#39;unixpwd&#39;)
</pre></div>
</div>
A slightly more advanced use of the reader — catching and reporting errors:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv, sys
filename = &#39;some.csv&#39;
with open(filename, &#39;rb&#39;) as f:
 reader = csv.reader(f)
 try:
 for row in reader:
 print row
 except csv.Error as e:
 sys.exit(&#39;file %s, line %d: %s&#39; % (filename, reader.line_num, e))
</pre></div>
</div>
And while the module doesn’t directly support parsing strings, it can easily be
done:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv
for row in csv.reader([&#39;one,two,three&#39;]):
 print row
</pre></div>
</div>
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">csv</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.
<code class="xref py py-func docutils literal notranslate">unicode_csv_reader()</code> below is a <a class="reference internal" href="../glossary.html#term-generator">generator</a> that wraps <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-class docutils literal notranslate">csv.reader</code></a>
to handle Unicode CSV data (a list of Unicode strings). <code class="xref py py-func docutils literal notranslate">utf_8_encoder()</code>
is a <a class="reference internal" href="../glossary.html#term-generator">generator</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">unicode_csv_reader()</code> decodes the UTF-8-encoded cells back into Unicode:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv

def unicode_csv_reader(unicode_csv_data, dialect=csv.excel, **kwargs):
 # csv.py doesn&#39;t do Unicode; encode temporarily as UTF-8:
 csv_reader = csv.reader(utf_8_encoder(unicode_csv_data),
 dialect=dialect, **kwargs)
 for row in csv_reader:
 # decode UTF-8 back to Unicode, cell by cell:
 yield [unicode(cell, &#39;utf-8&#39;) for cell in row]

def utf_8_encoder(unicode_csv_data):
 for line in unicode_csv_data:
 yield line.encode(&#39;utf-8&#39;)
</pre></div>
</div>
For all other encodings the following <code class="xref py py-class docutils literal notranslate">UnicodeReader</code> and
<code class="xref py py-class docutils literal notranslate">UnicodeWriter</code> classes can be used. They take an additional encoding
parameter in their constructor and make sure that the data passes the real
reader or writer encoded as UTF-8:
<div class="highlight-default notranslate"><div class="highlight"><pre>import csv, codecs, cStringIO

class UTF8Recoder:
 &quot;&quot;&quot;
 Iterator that reads an encoded stream and reencodes the input to UTF-8
 &quot;&quot;&quot;
 def __init__(self, f, encoding):
 self.reader = codecs.getreader(encoding)(f)

def __iter__(self):
 return self

def next(self):
 return self.reader.next().encode(&quot;utf-8&quot;)

class UnicodeReader:
 &quot;&quot;&quot;
 A CSV reader which will iterate over lines in the CSV file &quot;f&quot;,
 which is encoded in the given encoding.
 &quot;&quot;&quot;

def next(self):
 row = self.reader.next()
 return [unicode(s, &quot;utf-8&quot;) for s in row]

class UnicodeWriter:
 &quot;&quot;&quot;
 A CSV writer which will write rows to CSV file &quot;f&quot;,
 which is encoded in the given encoding.
 &quot;&quot;&quot;

def __init__(self, f, dialect=csv.excel, encoding=&quot;utf-8&quot;, **kwds):
 # Redirect output to a queue
 self.queue = cStringIO.StringIO()
 self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
 self.stream = f
 self.encoder = codecs.getincrementalencoder(encoding)()

def writerow(self, row):
 self.writer.writerow([s.encode(&quot;utf-8&quot;) for s in row])
 # Fetch UTF-8 output from the queue ...
 data = self.queue.getvalue()
 data = data.decode(&quot;utf-8&quot;)
 # ... and reencode it into the target encoding
 data = self.encoder.encode(data)
 # write to the target stream
 self.stream.write(data)
 # empty queue
 self.queue.truncate(0)

def writerows(self, rows):
 for row in rows:
 self.writerow(row)
</pre></div>
</div>
</section>
</section>

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<li><a class="reference internal" href="#">13.1. <code class="xref py py-mod docutils literal notranslate">csv</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>
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