.. 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.

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)

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*.