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 11 This module provides a simple interface to compress and decompress files just 12 like the GNU programs :program:`gzip` and :program:`gunzip` would. 13 14 The data compression is provided by the :mod:`zlib` module. 15 16 The :mod:`gzip` module provides the :class:`GzipFile` class which is modeled 17 after Python's File Object. The :class:`GzipFile` class reads and writes 18 :program:`gzip`\ -format files, automatically compressing or decompressing the 19 data so that it looks like an ordinary file object. 20 21 Note that additional file formats which can be decompressed by the 22 :program:`gzip` and :program:`gunzip` programs, such as those produced by 23 :program:`compress` and :program:`pack`, are not supported by this module. 24 25 The module defines the following items: 26 27 28 .. class:: GzipFile([filename[, mode[, compresslevel[, fileobj[, mtime]]]]]) 29 30 Constructor for the :class:`GzipFile` class, which simulates most of the methods 31 of a file object, with the exception of the :meth:`readinto` and 32 :meth:`truncate` methods. At least one of *fileobj* and *filename* must be 33 given a non-trivial value. 34 35 The new class instance is based on *fileobj*, which can be a regular file, a 36 :class:`~StringIO.StringIO` object, or any other object which simulates a file. It 37 defaults to ``None``, in which case *filename* is opened to provide a file 38 object. 39 40 When *fileobj* is not ``None``, the *filename* argument is only used to be 41 included in the :program:`gzip` file header, which may include the original 42 filename of the uncompressed file. It defaults to the filename of *fileobj*, if 43 discernible; otherwise, it defaults to the empty string, and in this case the 44 original filename is not included in the header. 45 46 The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``, ``'w'``, 47 or ``'wb'``, depending on whether the file will be read or written. The default 48 is the mode of *fileobj* if discernible; otherwise, the default is ``'rb'``. If 49 not given, the 'b' flag will be added to the mode to ensure the file is opened 50 in binary mode for cross-platform portability. 51 52 The *compresslevel* argument is an integer from ``0`` to ``9`` controlling 53 the level of compression; ``1`` is fastest and produces the least 54 compression, and ``9`` is slowest and produces the most compression. ``0`` 55 is no compression. The default is ``9``. 56 57 The *mtime* argument is an optional numeric timestamp to be written to 58 the stream when compressing. All :program:`gzip` compressed streams are 59 required to contain a timestamp. If omitted or ``None``, the current 60 time is used. This module ignores the timestamp when decompressing; 61 however, some programs, such as :program:`gunzip`\ , make use of it. 62 The format of the timestamp is the same as that of the return value of 63 ``time.time()`` and of the ``st_mtime`` attribute of the object returned 64 by ``os.stat()``. 65 66 Calling a :class:`GzipFile` object's :meth:`close` method does not close 67 *fileobj*, since you might wish to append more material after the compressed 68 data. This also allows you to pass a :class:`~StringIO.StringIO` object opened for 69 writing as *fileobj*, and retrieve the resulting memory buffer using the 70 :class:`~StringIO.StringIO` object's :meth:`~StringIO.StringIO.getvalue` method. 71 72 :class:`GzipFile` supports iteration and the :keyword:`with` statement. 73 74 .. versionchanged:: 2.7 75 Support for the :keyword:`with` statement was added. 76 77 .. versionchanged:: 2.7 78 Support for zero-padded files was added. 79 80 .. versionadded:: 2.7 81 The *mtime* argument. 82 83 84 .. function:: open(filename[, mode[, compresslevel]]) 85 86 This is a shorthand for ``GzipFile(filename,`` ``mode,`` ``compresslevel)``. 87 The *filename* argument is required; *mode* defaults to ``'rb'`` and 88 *compresslevel* defaults to ``9``. 89 90 91 .. _gzip-usage-examples: 92 93 Examples of usage 94 ----------------- 95 96 Example of how to read a compressed file:: 97 98 import gzip 99 with gzip.open('file.txt.gz', 'rb') as f: 100 file_content = f.read() 101 102 Example of how to create a compressed GZIP file:: 103 104 import gzip 105 content = "Lots of content here" 106 with gzip.open('file.txt.gz', 'wb') as f: 107 f.write(content) 108 109 Example of how to GZIP compress an existing file:: 110 111 import gzip 112 import shutil 113 with open('file.txt', 'rb') as f_in, gzip.open('file.txt.gz', 'wb') as f_out: 114 shutil.copyfileobj(f_in, f_out) 115 116 117 .. seealso:: 118 119 Module :mod:`zlib` 120 The basic data compression module needed to support the :program:`gzip` file 121 format. 122 123
