69 lines
3.1 KiB
ReStructuredText
69 lines
3.1 KiB
ReStructuredText
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: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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The data compression provided by the ``zlib`` module is compatible with that
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used by the GNU compression program :program:`gzip`. Accordingly, the
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:mod:`gzip` module provides the :class:`GzipFile` class to read and write
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:program:`gzip`\ -format files, automatically compressing or decompressing the
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data so it looks like an ordinary file object. Note that additional file
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formats which can be decompressed by the :program:`gzip` and :program:`gunzip`
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programs, such as those produced by :program:`compress` and :program:`pack`,
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are not supported by this module.
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The module defines the following items:
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.. class:: GzipFile([filename[, mode[, compresslevel[, fileobj]]]])
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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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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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.. function:: open(filename[, mode[, compresslevel]])
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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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.. 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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