1:mod:`gzip` --- Support for :program:`gzip` files
2=================================================
3
4.. module:: gzip
5   :synopsis: Interfaces for gzip compression and decompression using file objects.
6
7**Source code:** :source:`Lib/gzip.py`
8
9--------------
10
11This module provides a simple interface to compress and decompress files just
12like the GNU programs :program:`gzip` and :program:`gunzip` would.
13
14The data compression is provided by the :mod:`zlib` module.
15
16The :mod:`gzip` module provides the :class:`GzipFile` class, as well as the
17:func:`.open`, :func:`compress` and :func:`decompress` convenience functions.
18The :class:`GzipFile` class reads and writes :program:`gzip`\ -format files,
19automatically compressing or decompressing the data so that it looks like an
20ordinary :term:`file object`.
21
22Note that additional file formats which can be decompressed by the
23:program:`gzip` and :program:`gunzip` programs, such  as those produced by
24:program:`compress` and :program:`pack`, are not supported by this module.
25
26The module defines the following items:
27
28
29.. function:: open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)
30
31   Open a gzip-compressed file in binary or text mode, returning a :term:`file
32   object`.
33
34   The *filename* argument can be an actual filename (a :class:`str` or
35   :class:`bytes` object), or an existing file object to read from or write to.
36
37   The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``,
38   ``'w'``, ``'wb'``, ``'x'`` or ``'xb'`` for binary mode, or ``'rt'``,
39   ``'at'``, ``'wt'``, or ``'xt'`` for text mode. The default is ``'rb'``.
40
41   The *compresslevel* argument is an integer from 0 to 9, as for the
42   :class:`GzipFile` constructor.
43
44   For binary mode, this function is equivalent to the :class:`GzipFile`
45   constructor: ``GzipFile(filename, mode, compresslevel)``. In this case, the
46   *encoding*, *errors* and *newline* arguments must not be provided.
47
48   For text mode, a :class:`GzipFile` object is created, and wrapped in an
49   :class:`io.TextIOWrapper` instance with the specified encoding, error
50   handling behavior, and line ending(s).
51
52   .. versionchanged:: 3.3
53      Added support for *filename* being a file object, support for text mode,
54      and the *encoding*, *errors* and *newline* arguments.
55
56   .. versionchanged:: 3.4
57      Added support for the ``'x'``, ``'xb'`` and ``'xt'`` modes.
58
59   .. versionchanged:: 3.6
60      Accepts a :term:`path-like object`.
61
62.. class:: GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None)
63
64   Constructor for the :class:`GzipFile` class, which simulates most of the
65   methods of a :term:`file object`, with the exception of the :meth:`truncate`
66   method.  At least one of *fileobj* and *filename* must be given a non-trivial
67   value.
68
69   The new class instance is based on *fileobj*, which can be a regular file, an
70   :class:`io.BytesIO` object, or any other object which simulates a file.  It
71   defaults to ``None``, in which case *filename* is opened to provide a file
72   object.
73
74   When *fileobj* is not ``None``, the *filename* argument is only used to be
75   included in the :program:`gzip` file header, which may include the original
76   filename of the uncompressed file.  It defaults to the filename of *fileobj*, if
77   discernible; otherwise, it defaults to the empty string, and in this case the
78   original filename is not included in the header.
79
80   The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``, ``'w'``,
81   ``'wb'``, ``'x'``, or ``'xb'``, depending on whether the file will be read or
82   written.  The default is the mode of *fileobj* if discernible; otherwise, the
83   default is ``'rb'``.
84
85   Note that the file is always opened in binary mode. To open a compressed file
86   in text mode, use :func:`.open` (or wrap your :class:`GzipFile` with an
87   :class:`io.TextIOWrapper`).
88
89   The *compresslevel* argument is an integer from ``0`` to ``9`` controlling
90   the level of compression; ``1`` is fastest and produces the least
91   compression, and ``9`` is slowest and produces the most compression. ``0``
92   is no compression. The default is ``9``.
93
94   The *mtime* argument is an optional numeric timestamp to be written to
95   the last modification time field in the stream when compressing.  It
96   should only be provided in compression mode.  If omitted or ``None``, the
97   current time is used.  See the :attr:`mtime` attribute for more details.
98
99   Calling a :class:`GzipFile` object's :meth:`close` method does not close
100   *fileobj*, since you might wish to append more material after the compressed
101   data.  This also allows you to pass an :class:`io.BytesIO` object opened for
102   writing as *fileobj*, and retrieve the resulting memory buffer using the
103   :class:`io.BytesIO` object's :meth:`~io.BytesIO.getvalue` method.
104
105   :class:`GzipFile` supports the :class:`io.BufferedIOBase` interface,
106   including iteration and the :keyword:`with` statement.  Only the
107   :meth:`truncate` method isn't implemented.
108
109   :class:`GzipFile` also provides the following method and attribute:
110
111   .. method:: peek(n)
112
113      Read *n* uncompressed bytes without advancing the file position.
114      At most one single read on the compressed stream is done to satisfy
115      the call.  The number of bytes returned may be more or less than
116      requested.
117
118      .. note:: While calling :meth:`peek` does not change the file position of
119         the :class:`GzipFile`, it may change the position of the underlying
120         file object (e.g. if the :class:`GzipFile` was constructed with the
121         *fileobj* parameter).
122
123      .. versionadded:: 3.2
124
125   .. attribute:: mtime
126
127      When decompressing, the value of the last modification time field in
128      the most recently read header may be read from this attribute, as an
129      integer.  The initial value before reading any headers is ``None``.
130
131      All :program:`gzip` compressed streams are required to contain this
132      timestamp field.  Some programs, such as :program:`gunzip`\ , make use
133      of the timestamp.  The format is the same as the return value of
134      :func:`time.time` and the :attr:`~os.stat_result.st_mtime` attribute of
135      the object returned by :func:`os.stat`.
136
137   .. versionchanged:: 3.1
138      Support for the :keyword:`with` statement was added, along with the
139      *mtime* constructor argument and :attr:`mtime` attribute.
140
141   .. versionchanged:: 3.2
142      Support for zero-padded and unseekable files was added.
143
144   .. versionchanged:: 3.3
145      The :meth:`io.BufferedIOBase.read1` method is now implemented.
146
147   .. versionchanged:: 3.4
148      Added support for the ``'x'`` and ``'xb'`` modes.
149
150   .. versionchanged:: 3.5
151      Added support for writing arbitrary
152      :term:`bytes-like objects <bytes-like object>`.
153      The :meth:`~io.BufferedIOBase.read` method now accepts an argument of
154      ``None``.
155
156   .. versionchanged:: 3.6
157      Accepts a :term:`path-like object`.
158
159
160.. function:: compress(data, compresslevel=9)
161
162   Compress the *data*, returning a :class:`bytes` object containing
163   the compressed data.  *compresslevel* has the same meaning as in
164   the :class:`GzipFile` constructor above.
165
166   .. versionadded:: 3.2
167
168.. function:: decompress(data)
169
170   Decompress the *data*, returning a :class:`bytes` object containing the
171   uncompressed data.
172
173   .. versionadded:: 3.2
174
175
176.. _gzip-usage-examples:
177
178Examples of usage
179-----------------
180
181Example of how to read a compressed file::
182
183   import gzip
184   with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
185       file_content = f.read()
186
187Example of how to create a compressed GZIP file::
188
189   import gzip
190   content = b"Lots of content here"
191   with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
192       f.write(content)
193
194Example of how to GZIP compress an existing file::
195
196   import gzip
197   import shutil
198   with open('/home/joe/file.txt', 'rb') as f_in:
199       with gzip.open('/home/joe/file.txt.gz', 'wb') as f_out:
200           shutil.copyfileobj(f_in, f_out)
201
202Example of how to GZIP compress a binary string::
203
204   import gzip
205   s_in = b"Lots of content here"
206   s_out = gzip.compress(s_in)
207
208.. seealso::
209
210   Module :mod:`zlib`
211      The basic data compression module needed to support the :program:`gzip` file
212      format.
213
214