1 :mod:`gzip` --- Support for :program:`gzip` files
2 =================================================
5 :synopsis: Interfaces for gzip compression and decompression using file objects.
7 This module provides a simple interface to compress and decompress files just
8 like the GNU programs :program:`gzip` and :program:`gunzip` would.
10 The data compression is provided by the :mod:`zlib` module.
12 The :mod:`gzip` module provides the :class:`GzipFile` class which is modeled
13 after Python's File Object. The :class:`GzipFile` class reads and writes
14 :program:`gzip`\ -format files, automatically compressing or decompressing the
15 data so that it looks like an ordinary file object.
17 Note that additional file formats which can be decompressed by the
18 :program:`gzip` and :program:`gunzip` programs, such as those produced by
19 :program:`compress` and :program:`pack`, are not supported by this module.
21 For other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and
22 :mod:`tarfile` modules.
24 The module defines the following items:
27 .. class:: GzipFile([filename[, mode[, compresslevel[, fileobj[, mtime]]]]])
29 Constructor for the :class:`GzipFile` class, which simulates most of the methods
30 of a file object, with the exception of the :meth:`readinto` and
31 :meth:`truncate` methods. At least one of *fileobj* and *filename* must be
32 given a non-trivial value.
34 The new class instance is based on *fileobj*, which can be a regular file, a
35 :class:`StringIO` object, or any other object which simulates a file. It
36 defaults to ``None``, in which case *filename* is opened to provide a file
39 When *fileobj* is not ``None``, the *filename* argument is only used to be
40 included in the :program:`gzip` file header, which may includes the original
41 filename of the uncompressed file. It defaults to the filename of *fileobj*, if
42 discernible; otherwise, it defaults to the empty string, and in this case the
43 original filename is not included in the header.
45 The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``, ``'w'``,
46 or ``'wb'``, depending on whether the file will be read or written. The default
47 is the mode of *fileobj* if discernible; otherwise, the default is ``'rb'``. If
48 not given, the 'b' flag will be added to the mode to ensure the file is opened
49 in binary mode for cross-platform portability.
51 The *compresslevel* argument is an integer from ``1`` to ``9`` controlling the
52 level of compression; ``1`` is fastest and produces the least compression, and
53 ``9`` is slowest and produces the most compression. The default is ``9``.
55 The *mtime* argument is an optional numeric timestamp to be written to
56 the stream when compressing. All :program:`gzip` compressed streams are
57 required to contain a timestamp. If omitted or ``None``, the current
58 time is used. This module ignores the timestamp when decompressing;
59 however, some programs, such as :program:`gunzip`\ , make use of it.
60 The format of the timestamp is the same as that of the return value of
61 ``time.time()`` and of the ``st_mtime`` member of the object returned
64 Calling a :class:`GzipFile` object's :meth:`close` method does not close
65 *fileobj*, since you might wish to append more material after the compressed
66 data. This also allows you to pass a :class:`StringIO` object opened for
67 writing as *fileobj*, and retrieve the resulting memory buffer using the
68 :class:`StringIO` object's :meth:`getvalue` method.
70 :class:`GzipFile` supports the :keyword:`with` statement.
72 .. versionchanged:: 2.7
73 Support for the :keyword:`with` statement was added.
76 .. function:: open(filename[, mode[, compresslevel]])
78 This is a shorthand for ``GzipFile(filename,`` ``mode,`` ``compresslevel)``.
79 The *filename* argument is required; *mode* defaults to ``'rb'`` and
80 *compresslevel* defaults to ``9``.
83 .. _gzip-usage-examples:
88 Example of how to read a compressed file::
91 f = gzip.open('/home/joe/file.txt.gz', 'rb')
92 file_content = f.read()
95 Example of how to create a compressed GZIP file::
98 content = "Lots of content here"
99 f = gzip.open('/home/joe/file.txt.gz', 'wb')
103 Example of how to GZIP compress an existing file::
106 f_in = open('/home/joe/file.txt', 'rb')
107 f_out = gzip.open('/home/joe/file.txt.gz', 'wb')
108 f_out.writelines(f_in)
116 The basic data compression module needed to support the :program:`gzip` file