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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

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<title>14.1. csv — CSV File Reading and Writing — Python 3.7.0 說明文件</title>

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<h1>14.1. <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="本標題的永久連結">¶</a></h1>

Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/csv.py">Lib/csv.py</a>

The so-called CSV (Comma Separated Values) format is the most common import and

export format for spreadsheets and databases. CSV format was used for many

years prior to attempts to describe the format in a standardized way in

<a class="rfc reference external" href="https://tools.ietf.org/html/rfc4180.html">RFC 4180</a>. The lack of a well-defined 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.

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.

也參考

<dd>The Python Enhancement Proposal which proposed this addition to Python.</dd>

</dl>

</div>

<h2>14.1.1. Module Contents<a class="headerlink" href="#module-contents" title="本標題的永久連結">¶</a></h2>

<code class="descclassname">csv.</code><code class="descname">reader</code>(csvfile, dialect='excel', **fmtparams)<a class="headerlink" href="#csv.reader" title="本定義的永久連結">¶</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 — <a class="reference internal" href="../glossary.html#term-file-object">file objects</a> and list objects are both suitable. If csvfile is a file object,

it should be opened with <code class="docutils literal notranslate">newline=''</code>. <a class="footnote-reference" href="#id3" id="id1">[1]</a> 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 unless the <code class="docutils literal notranslate">QUOTE_NONNUMERIC</code> format

option is specified (in which case unquoted fields are transformed into floats).

A short usage example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> import csv

>>> with open('eggs.csv', newline='') as csvfile:

... spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|')

... for row in spamreader:

... print(', '.join(row))

Spam, Spam, Spam, Spam, Spam, Baked Beans

Spam, Lovely Spam, Wonderful Spam

</pre></div>

</div>

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">writer</code>(csvfile, dialect='excel', **fmtparams)<a class="headerlink" href="#csv.writer" title="本定義的永久連結">¶</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 should be opened with

<code class="docutils literal notranslate">newline=''</code> <a class="footnote-reference" href="#id3" id="id2">[1]</a>. 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

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.

All other non-string data are stringified with <a class="reference internal" href="stdtypes.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-python3 notranslate"><div class="highlight"><pre>import csv

with open('eggs.csv', 'w', newline='') as csvfile:

spamwriter = csv.writer(csvfile, delimiter=' ',

quotechar='|', quoting=csv.QUOTE_MINIMAL)

spamwriter.writerow(['Spam'] * 5 + ['Baked Beans'])

spamwriter.writerow(['Spam', 'Lovely Spam', 'Wonderful Spam'])

</pre></div>

</div>

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">register_dialect</code>(name[, dialect[, **fmtparams]])<a class="headerlink" href="#csv.register_dialect" title="本定義的永久連結">¶</a></dt>

<dd>Associate dialect with name. name must be a string. 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>

<code class="descclassname">csv.</code><code class="descname">unregister_dialect</code>(name)<a class="headerlink" href="#csv.unregister_dialect" title="本定義的永久連結">¶</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>

<code class="descclassname">csv.</code><code class="descname">get_dialect</code>(name)<a class="headerlink" href="#csv.get_dialect" title="本定義的永久連結">¶</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. This function 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>.

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">list_dialects</code>()<a class="headerlink" href="#csv.list_dialects" title="本定義的永久連結">¶</a></dt>

<dd>Return the names of all registered dialects.

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">field_size_limit</code>([new_limit])<a class="headerlink" href="#csv.field_size_limit" title="本定義的永久連結">¶</a></dt>

<dd>Returns the current maximum field size allowed by the parser. If new_limit is

given, this becomes the new limit.

</dd></dl>

class <code class="descclassname">csv.</code><code class="descname">DictReader</code>(f, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)<a class="headerlink" href="#csv.DictReader" title="本定義的永久連結">¶</a></dt>

<dd>Create an object that operates like a regular reader but maps the

information in each row to an <a class="reference internal" href="collections.html#collections.OrderedDict" title="collections.OrderedDict"><code class="xref py py-mod docutils literal notranslate">OrderedDict</code></a>

whose keys are given by the optional fieldnames parameter.

The fieldnames parameter is a <a class="reference internal" href="../glossary.html#term-sequence">sequence</a>. If fieldnames is

omitted, the values in the first row of file f will be used as the

fieldnames. Regardless of how the fieldnames are determined, the ordered

dictionary preserves their original ordering.

If a row has more fields than fieldnames, the remaining data is put in a

list and stored with the fieldname specified by restkey (which defaults

to <code class="docutils literal notranslate">None</code>). If a non-blank row has fewer fields than fieldnames, the

missing values are filled-in with <code class="docutils literal notranslate">None</code>.

All 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.

3.6 版更變: Returned rows are now of type <code class="xref py py-class docutils literal notranslate">OrderedDict</code>.

</div>

A short usage example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> import csv

>>> with open('names.csv', newline='') as csvfile:

... reader = csv.DictReader(csvfile)

... for row in reader:

... print(row['first_name'], row['last_name'])

...

Eric Idle

John Cleese

>>> print(row)

OrderedDict([('first_name', 'John'), ('last_name', 'Cleese')])

</pre></div>

</div>

</dd></dl>

class <code class="descclassname">csv.</code><code class="descname">DictWriter</code>(f, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)<a class="headerlink" href="#csv.DictWriter" title="本定義的永久連結">¶</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.abc.html#module-collections.abc" title="collections.abc: Abstract base classes for containers"><code class="xref py py-mod docutils literal notranslate">sequence</code></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 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>, the default value, a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>

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> class is not optional.

A short usage example:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

with open('names.csv', 'w', newline='') as csvfile:

fieldnames = ['first_name', 'last_name']

writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

writer.writeheader()

writer.writerow({'first_name': 'Baked', 'last_name': 'Beans'})

writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})

writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})

</pre></div>

</div>

</dd></dl>

class <code class="descclassname">csv.</code><code class="descname">Dialect</code><a class="headerlink" href="#csv.Dialect" title="本定義的永久連結">¶</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>

class <code class="descclassname">csv.</code><code class="descname">excel</code><a class="headerlink" href="#csv.excel" title="本定義的永久連結">¶</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>

class <code class="descclassname">csv.</code><code class="descname">excel_tab</code><a class="headerlink" href="#csv.excel_tab" title="本定義的永久連結">¶</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>

class <code class="descclassname">csv.</code><code class="descname">unix_dialect</code><a class="headerlink" href="#csv.unix_dialect" title="本定義的永久連結">¶</a></dt>

<dd>The <a class="reference internal" href="#csv.unix_dialect" title="csv.unix_dialect"><code class="xref py py-class docutils literal notranslate">unix_dialect</code></a> class defines the usual properties of a CSV file

generated on UNIX systems, i.e. using <code class="docutils literal notranslate">'\n'</code> as line terminator and quoting

all fields. It is registered with the dialect name <code class="docutils literal notranslate">'unix'</code>.

3.2 版新加入.

</div>

</dd></dl>

class <code class="descclassname">csv.</code><code class="descname">Sniffer</code><a class="headerlink" href="#csv.Sniffer" title="本定義的永久連結">¶</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:

<code class="descname">sniff</code>(sample, delimiters=None)<a class="headerlink" href="#csv.Sniffer.sniff" title="本定義的永久連結">¶</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>

<code class="descname">has_header</code>(sample)<a class="headerlink" href="#csv.Sniffer.has_header" title="本定義的永久連結">¶</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>

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-python3 notranslate"><div class="highlight"><pre>with open('example.csv', newline='') as csvfile:

dialect = csv.Sniffer().sniff(csvfile.read(1024))

csvfile.seek(0)

# ... process CSV file contents here ...

</pre></div>

</div>

<code class="descclassname">csv.</code><code class="descname">QUOTE_ALL</code><a class="headerlink" href="#csv.QUOTE_ALL" title="本定義的永久連結">¶</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>

<code class="descclassname">csv.</code><code class="descname">QUOTE_MINIMAL</code><a class="headerlink" href="#csv.QUOTE_MINIMAL" title="本定義的永久連結">¶</a></dt>

special characters such as delimiter, quotechar or any of the characters in

lineterminator.

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">QUOTE_NONNUMERIC</code><a class="headerlink" href="#csv.QUOTE_NONNUMERIC" title="本定義的永久連結">¶</a></dt>

Instructs the reader to convert all non-quoted fields to type float.

</dd></dl>

<code class="descclassname">csv.</code><code class="descname">QUOTE_NONE</code><a class="headerlink" href="#csv.QUOTE_NONE" title="本定義的永久連結">¶</a></dt>

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>

exception <code class="descclassname">csv.</code><code class="descname">Error</code><a class="headerlink" href="#csv.Error" title="本定義的永久連結">¶</a></dt>

<dd>Raised by any of the functions when an error is detected.

</dd></dl>

</div>

<h2>14.1.2. Dialects and Formatting Parameters<a class="headerlink" href="#dialects-and-formatting-parameters" title="本標題的永久連結">¶</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

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:

<code class="descclassname">Dialect.</code><code class="descname">delimiter</code><a class="headerlink" href="#csv.Dialect.delimiter" title="本定義的永久連結">¶</a></dt>

<dd>A one-character string used to separate fields. It defaults to <code class="docutils literal notranslate">','</code>.

</dd></dl>

<code class="descclassname">Dialect.</code><code class="descname">doublequote</code><a class="headerlink" href="#csv.Dialect.doublequote" title="本定義的永久連結">¶</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,

</dd></dl>

<code class="descclassname">Dialect.</code><code class="descname">escapechar</code><a class="headerlink" href="#csv.Dialect.escapechar" title="本定義的永久連結">¶</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>

<code class="descclassname">Dialect.</code><code class="descname">lineterminator</code><a class="headerlink" href="#csv.Dialect.lineterminator" title="本定義的永久連結">¶</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>.

備註

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>

<code class="descclassname">Dialect.</code><code class="descname">quotechar</code><a class="headerlink" href="#csv.Dialect.quotechar" title="本定義的永久連結">¶</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">'"'</code>.

</dd></dl>

<code class="descclassname">Dialect.</code><code class="descname">quoting</code><a class="headerlink" href="#csv.Dialect.quoting" title="本定義的永久連結">¶</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>

<code class="descclassname">Dialect.</code><code class="descname">skipinitialspace</code><a class="headerlink" href="#csv.Dialect.skipinitialspace" title="本定義的永久連結">¶</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>

<code class="descclassname">Dialect.</code><code class="descname">strict</code><a class="headerlink" href="#csv.Dialect.strict" title="本定義的永久連結">¶</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>

</div>

<h2>14.1.3. Reader Objects<a class="headerlink" href="#reader-objects" title="本標題的永久連結">¶</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:

<code class="descclassname">csvreader.</code><code class="descname">__next__</code>()<a class="headerlink" href="#csv.csvreader.__next__" title="本定義的永久連結">¶</a></dt>

<dd>Return the next row of the reader’s iterable object as a list (if the object

was returned from <a class="reference internal" href="#csv.reader" title="csv.reader"><code class="xref py py-func docutils literal notranslate">reader()</code></a>) or a dict (if it is a <a class="reference internal" href="#csv.DictReader" title="csv.DictReader"><code class="xref py py-class docutils literal notranslate">DictReader</code></a>

instance), parsed according to the current dialect. Usually you should call

this as <code class="docutils literal notranslate">next(reader)</code>.

</dd></dl>

Reader objects have the following public attributes:

<code class="descclassname">csvreader.</code><code class="descname">dialect</code><a class="headerlink" href="#csv.csvreader.dialect" title="本定義的永久連結">¶</a></dt>

<dd>A read-only description of the dialect in use by the parser.

</dd></dl>

<code class="descclassname">csvreader.</code><code class="descname">line_num</code><a class="headerlink" href="#csv.csvreader.line_num" title="本定義的永久連結">¶</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.

</dd></dl>

DictReader objects have the following public attribute:

<code class="descclassname">csvreader.</code><code class="descname">fieldnames</code><a class="headerlink" href="#csv.csvreader.fieldnames" title="本定義的永久連結">¶</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.

</dd></dl>

</div>

<h2>14.1.4. Writer Objects<a class="headerlink" href="#writer-objects" title="本標題的永久連結">¶</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

an iterable 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="stdtypes.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).

<code class="descclassname">csvwriter.</code><code class="descname">writerow</code>(row)<a class="headerlink" href="#csv.csvwriter.writerow" title="本定義的永久連結">¶</a></dt>

<dd>Write the row parameter to the writer’s file object, formatted according to

the current dialect.

3.5 版更變: Added support of arbitrary iterables.

</div>

</dd></dl>

<code class="descclassname">csvwriter.</code><code class="descname">writerows</code>(rows)<a class="headerlink" href="#csv.csvwriter.writerows" title="本定義的永久連結">¶</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:

<code class="descclassname">csvwriter.</code><code class="descname">dialect</code><a class="headerlink" href="#csv.csvwriter.dialect" title="本定義的永久連結">¶</a></dt>

<dd>A read-only description of the dialect in use by the writer.

</dd></dl>

DictWriter objects have the following public method:

<code class="descclassname">DictWriter.</code><code class="descname">writeheader</code>()<a class="headerlink" href="#csv.DictWriter.writeheader" title="本定義的永久連結">¶</a></dt>

<dd>Write a row with the field names (as specified in the constructor).

3.2 版新加入.

</div>

</dd></dl>

</div>

<h2>14.1.5. Examples<a class="headerlink" href="#examples" title="本標題的永久連結">¶</a></h2>

The simplest example of reading a CSV file:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

with open('some.csv', newline='') as f:

for row in reader:

print(row)

</pre></div>

</div>

Reading a file with an alternate format:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

with open('passwd', newline='') as f:

reader = csv.reader(f, delimiter=':', quoting=csv.QUOTE_NONE)

for row in reader:

print(row)

</pre></div>

</div>

The corresponding simplest possible writing example is:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

with open('some.csv', 'w', newline='') as f:

writer = csv.writer(f)

writer.writerows(someiterable)

</pre></div>

</div>

Since <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> is used to open a CSV file for reading, the file

will by default be decoded into unicode using the system default

encoding (see <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><code class="xref py py-func docutils literal notranslate">locale.getpreferredencoding()</code></a>). To decode a file

using a different encoding, use the <code class="docutils literal notranslate">encoding</code> argument of open:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

with open('some.csv', newline='', encoding='utf-8') as f:

for row in reader:

print(row)

</pre></div>

</div>

The same applies to writing in something other than the system default

encoding: specify the encoding argument when opening the output file.

Registering a new dialect:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv

csv.register_dialect('unixpwd', delimiter=':', quoting=csv.QUOTE_NONE)

</pre></div>

</div>

A slightly more advanced use of the reader — catching and reporting errors:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import csv, sys

filename = 'some.csv'

with open(filename, newline='') as f:

try:

for row in reader:

print(row)

except csv.Error as e:

sys.exit('file {}, line {}: {}'.format(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-python3 notranslate"><div class="highlight"><pre>import csv

for row in csv.reader(['one,two,three']):

print(row)

</pre></div>

</div>

註解

<tr><td class="label">[1]</td><td>(<a class="fn-backref" href="#id1">1</a>, <a class="fn-backref" href="#id2">2</a>) If <code class="docutils literal notranslate">newline=''</code> is not specified, newlines embedded inside quoted fields

will not be interpreted correctly, and on platforms that use <code class="docutils literal notranslate">\r\n</code> linendings

on write an extra <code class="docutils literal notranslate">\r</code> will be added. It should always be safe to specify

<code class="docutils literal notranslate">newline=''</code>, since the csv module does its own

(<a class="reference internal" href="../glossary.html#term-universal-newlines">universal</a>) newline handling.</td></tr>

</tbody>

</table>

</div>

<ul>

<li><a class="reference internal" href="#">14.1. <code class="docutils literal notranslate">csv</code> — CSV File Reading and Writing</a><ul>

<li><a class="reference internal" href="#module-contents">14.1.1. Module Contents</a></li>

<li><a class="reference internal" href="#dialects-and-formatting-parameters">14.1.2. Dialects and Formatting Parameters</a></li>

<li><a class="reference internal" href="#reader-objects">14.1.3. Reader Objects</a></li>

<li><a class="reference internal" href="#writer-objects">14.1.4. Writer Objects</a></li>

<li><a class="reference internal" href="#examples">14.1.5. Examples</a></li>

</ul>

</li>

</ul>

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