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:mod:`gzip` --- Support for :program:`gzip` files
=================================================
.. module:: gzip
:synopsis: Interfaces for gzip compression and decompression using file objects.
The data compression provided by the ``zlib`` module is compatible with that
used by the GNU compression program :program:`gzip`. Accordingly, the
:mod:`gzip` module provides the :class:`GzipFile` class to read and write
:program:`gzip`\ -format files, automatically compressing or decompressing the
data so it looks like an ordinary file object. Note that additional file
formats which can be decompressed by the :program:`gzip` and :program:`gunzip`
programs, such as those produced by :program:`compress` and :program:`pack`,
are not supported by this module.
For other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and
:mod:`tarfile` modules.
The module defines the following items:
.. class:: GzipFile([filename[, mode[, compresslevel[, fileobj]]]])
Constructor for the :class:`GzipFile` class, which simulates most of the methods
of a file object, with the exception of the :meth:`readinto` and
:meth:`truncate` methods. At least one of *fileobj* and *filename* must be
given a non-trivial value.
The new class instance is based on *fileobj*, which can be a regular file, a
:class:`StringIO` object, or any other object which simulates a file. It
defaults to ``None``, in which case *filename* is opened to provide a file
object.
When *fileobj* is not ``None``, the *filename* argument is only used to be
included in the :program:`gzip` file header, which may includes the original
filename of the uncompressed file. It defaults to the filename of *fileobj*, if
discernible; otherwise, it defaults to the empty string, and in this case the
original filename is not included in the header.
The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``, ``'w'``,
or ``'wb'``, depending on whether the file will be read or written. The default
is the mode of *fileobj* if discernible; otherwise, the default is ``'rb'``. If
not given, the 'b' flag will be added to the mode to ensure the file is opened
in binary mode for cross-platform portability.
The *compresslevel* argument is an integer from ``1`` to ``9`` controlling the
level of compression; ``1`` is fastest and produces the least compression, and
``9`` is slowest and produces the most compression. The default is ``9``.
Calling a :class:`GzipFile` object's :meth:`close` method does not close
*fileobj*, since you might wish to append more material after the compressed
data. This also allows you to pass a :class:`StringIO` object opened for
writing as *fileobj*, and retrieve the resulting memory buffer using the
:class:`StringIO` object's :meth:`getvalue` method.
.. function:: open(filename[, mode[, compresslevel]])
This is a shorthand for ``GzipFile(filename,`` ``mode,`` ``compresslevel)``.
The *filename* argument is required; *mode* defaults to ``'rb'`` and
*compresslevel* defaults to ``9``.
.. seealso::
Module :mod:`zlib`
The basic data compression module needed to support the :program:`gzip` file
format.
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