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118 lines
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ReStructuredText
118 lines
4.6 KiB
ReStructuredText
:mod:`gzip` --- Support for :program:`gzip` files
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=================================================
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.. module:: gzip
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:synopsis: Interfaces for gzip compression and decompression using file objects.
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This module provides a simple interface to compress and decompress files just
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like the GNU programs :program:`gzip` and :program:`gunzip` would.
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The data compression is provided by the :mod:`zlib` module.
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The :mod:`gzip` module provides the :class:`GzipFile` class which is modeled
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after Python's File Object. The :class:`GzipFile` class reads and writes
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:program:`gzip`\ -format files, automatically compressing or decompressing the
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data so that it looks like an ordinary file object.
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Note that additional file formats which can be decompressed by the
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:program:`gzip` and :program:`gunzip` programs, such as those produced by
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:program:`compress` and :program:`pack`, are not supported by this module.
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For other archive formats, see the :mod:`bz2`, :mod:`zipfile`, and
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:mod:`tarfile` modules.
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The module defines the following items:
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.. class:: GzipFile(filename=None, mode=None, compresslevel=9, fileobj=None, mtime=None)
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Constructor for the :class:`GzipFile` class, which simulates most of the methods
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of a file object, with the exception of the :meth:`readinto` and
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:meth:`truncate` methods. At least one of *fileobj* and *filename* must be
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given a non-trivial value.
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The new class instance is based on *fileobj*, which can be a regular file, a
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:class:`StringIO` object, or any other object which simulates a file. It
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defaults to ``None``, in which case *filename* is opened to provide a file
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object.
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When *fileobj* is not ``None``, the *filename* argument is only used to be
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included in the :program:`gzip` file header, which may includes the original
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filename of the uncompressed file. It defaults to the filename of *fileobj*, if
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discernible; otherwise, it defaults to the empty string, and in this case the
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original filename is not included in the header.
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The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``, ``'w'``,
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or ``'wb'``, depending on whether the file will be read or written. The default
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is the mode of *fileobj* if discernible; otherwise, the default is ``'rb'``. If
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not given, the 'b' flag will be added to the mode to ensure the file is opened
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in binary mode for cross-platform portability.
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The *compresslevel* argument is an integer from ``1`` to ``9`` controlling the
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level of compression; ``1`` is fastest and produces the least compression, and
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``9`` is slowest and produces the most compression. The default is ``9``.
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The *mtime* argument is an optional numeric timestamp to be written to
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the stream when compressing. All :program:`gzip` compressed streams are
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required to contain a timestamp. If omitted or ``None``, the current
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time is used. This module ignores the timestamp when decompressing;
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however, some programs, such as :program:`gunzip`\ , make use of it.
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The format of the timestamp is the same as that of the return value of
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``time.time()`` and of the ``st_mtime`` member of the object returned
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by ``os.stat()``.
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Calling a :class:`GzipFile` object's :meth:`close` method does not close
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*fileobj*, since you might wish to append more material after the compressed
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data. This also allows you to pass a :class:`StringIO` object opened for
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writing as *fileobj*, and retrieve the resulting memory buffer using the
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:class:`StringIO` object's :meth:`getvalue` method.
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:class:`GzipFile` supports the :keyword:`with` statement.
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.. versionchanged:: 3.1
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Support for the :keyword:`with` statement was added.
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.. function:: open(filename, mode='rb', compresslevel=9)
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This is a shorthand for ``GzipFile(filename,`` ``mode,`` ``compresslevel)``.
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The *filename* argument is required; *mode* defaults to ``'rb'`` and
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*compresslevel* defaults to ``9``.
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.. _gzip-usage-examples:
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Examples of usage
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-----------------
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Example of how to read a compressed file::
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import gzip
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f = gzip.open('/home/joe/file.txt.gz', 'rb')
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file_content = f.read()
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f.close()
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Example of how to create a compressed GZIP file::
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import gzip
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content = "Lots of content here"
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f = gzip.open('/home/joe/file.txt.gz', 'wb')
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f.write(content)
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f.close()
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Example of how to GZIP compress an existing file::
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import gzip
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f_in = open('/home/joe/file.txt', 'rb')
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f_out = gzip.open('/home/joe/file.txt.gz', 'wb')
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f_out.writelines(f_in)
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f_out.close()
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f_in.close()
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.. seealso::
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Module :mod:`zlib`
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The basic data compression module needed to support the :program:`gzip` file
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format.
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