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:mod:`gzip` --- Support for :program:`gzip` files
=================================================
.. module:: gzip
:synopsis: Interfaces for gzip compression and decompression using file objects.
This module provides a simple interface to compress and decompress files just
like the GNU programs :program:`gzip` and :program:`gunzip` would.
The data compression is provided by the :mod:`zlib` module.
The :mod:`gzip` module provides the :class:`GzipFile` class. The :class:`GzipFile`
class reads and writes :program:`gzip`\ -format files, automatically compressing
or decompressing the data so that it looks like an ordinary :term:`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=None, mode=None, compresslevel=9, fileobj=None, mtime=None)
Constructor for the :class:`GzipFile` class, which simulates most of the methods
of a :term:`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``.
The *mtime* argument is an optional numeric timestamp to be written to
the stream when compressing. All :program:`gzip` compressed streams are
required to contain a timestamp. If omitted or ``None``, the current
time is used. This module ignores the timestamp when decompressing;
however, some programs, such as :program:`gunzip`\ , make use of it.
The format of the timestamp is the same as that of the return value of
``time.time()`` and of the ``st_mtime`` member of the object returned
by ``os.stat()``.
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:`io.BytesIO` object opened for
writing as *fileobj*, and retrieve the resulting memory buffer using the
:class:`io.BytesIO` object's :meth:`~io.BytesIO.getvalue` method.
:class:`GzipFile` supports the whole :class:`io.BufferedIOBase` interface,
including iteration and the :keyword:`with` statement.
.. versionchanged:: 3.1
Support for the :keyword:`with` statement was added.
.. versionchanged:: 3.2
Support for zero-padded files was added.
.. versionchanged:: 3.2
Support for unseekable files was added.
.. function:: open(filename, mode='rb', compresslevel=9)
This is a shorthand for ``GzipFile(filename,`` ``mode,`` ``compresslevel)``.
The *filename* argument is required; *mode* defaults to ``'rb'`` and
*compresslevel* defaults to ``9``.
.. function:: compress(data, compresslevel=9)
Compress the *data*, returning a :class:`bytes` object containing
the compressed data. *compresslevel* has the same meaning as in
the :class:`GzipFile` constructor above.
.. versionadded:: 3.2
.. function:: decompress(data)
Decompress the *data*, returning a :class:`bytes` object containing the
uncompressed data.
.. versionadded:: 3.2
.. _gzip-usage-examples:
Examples of usage
-----------------
Example of how to read a compressed file::
import gzip
with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
file_content = f.read()
Example of how to create a compressed GZIP file::
import gzip
content = b"Lots of content here"
with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
f.write(content)
Example of how to GZIP compress an existing file::
import gzip
with open('/home/joe/file.txt', 'rb') as f_in:
with gzip.open('/home/joe/file.txt.gz', 'wb') as f_out:
f_out.writelines(f_in)
Example of how to GZIP compress a binary string::
import gzip
s_in = b"Lots of content here"
s_out = gzip.compress(s_in)
.. seealso::
Module :mod:`zlib`
The basic data compression module needed to support the :program:`gzip` file
format.
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