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Merge #20628: make it clear that DictReader/Writer *fieldnames* is a Sequence. 

Including the subsequent line re-wrapping.
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R David Murray 2014-02-24 15:34:48 -05:00
parent c5f5e625aa f031a6f334
commit 4f91364598
1 changed files with 32 additions and 25 deletions
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Doc/library/csv.rst
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@ -142,36 +142,43 @@ The :mod:`csv` module defines the following functions:
The :mod:`csv` module defines the following classes:
.. class:: DictReader(csvfile, fieldnames=None, restkey=None, restval=None, dialect='excel', *args, **kwds)
.. class:: DictReader(csvfile, fieldnames=None, restkey=None, restval=None, \
dialect='excel', *args, **kwds)
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.
If the *fieldnames* parameter is omitted, the values in the first row of the
*csvfile* 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 :class:`reader` instance.
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 :mod:`sequence
<collections.abc>` 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 *csvfile* 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 :class:`reader` instance.
.. class:: DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)
.. class:: DictWriter(csvfile, fieldnames, restval='', extrasaction='raise', \
dialect='excel', *args, **kwds)
Create an object which operates like a regular writer but maps dictionaries onto
output rows. The *fieldnames* parameter identifies the order in which values in
the dictionary passed to the :meth:`writerow` method are written to the
*csvfile*. 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 :meth:`writerow` method contains a key not found in *fieldnames*, the
optional *extrasaction* parameter indicates what action to take. If it is set
to ``'raise'`` a :exc:`ValueError` is raised. If it is set to ``'ignore'``,
extra values in the dictionary are ignored. Any other optional or keyword
arguments are passed to the underlying :class:`writer` instance.
Create an object which operates like a regular writer but maps dictionaries
onto output rows. The *fieldnames* parameter is a :mod:`sequence
<collections.abc>` of keys that identify the order in which values in the
dictionary passed to the :meth:`writerow` method are written to the
*csvfile*. 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 :meth:`writerow` method contains a key not found in
*fieldnames*, the optional *extrasaction* parameter indicates what action to
take. If it is set to ``'raise'`` a :exc:`ValueError` is raised. If it is
set to ``'ignore'``, extra values in the dictionary are ignored. Any other
optional or keyword arguments are passed to the underlying :class:`writer`
instance.
Note that unlike the :class:`DictReader` class, the *fieldnames* parameter of
the :class:`DictWriter` is not optional. Since Python's :class:`dict` objects
are not ordered, there is not enough information available to deduce the order
in which the row should be written to the *csvfile*.
Note that unlike the :class:`DictReader` class, the *fieldnames* parameter
of the :class:`DictWriter` is not optional. Since Python's :class:`dict`
objects are not ordered, there is not enough information available to deduce
the order in which the row should be written to the *csvfile*.
.. class:: Dialect