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214 lines
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ReStructuredText
214 lines
8.1 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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**Source code:** :source:`Lib/gzip.py`
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--------------
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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, as well as the
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:func:`.open`, :func:`compress` and :func:`decompress` convenience functions.
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The :class:`GzipFile` class reads and writes :program:`gzip`\ -format files,
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automatically compressing or decompressing the data so that it looks like an
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ordinary :term:`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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The module defines the following items:
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.. function:: open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)
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Open a gzip-compressed file in binary or text mode, returning a :term:`file
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object`.
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The *filename* argument can be an actual filename (a :class:`str` or
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:class:`bytes` object), or an existing file object to read from or write to.
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The *mode* argument can be any of ``'r'``, ``'rb'``, ``'a'``, ``'ab'``,
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``'w'``, ``'wb'``, ``'x'`` or ``'xb'`` for binary mode, or ``'rt'``,
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``'at'``, ``'wt'``, or ``'xt'`` for text mode. The default is ``'rb'``.
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The *compresslevel* argument is an integer from 0 to 9, as for the
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:class:`GzipFile` constructor.
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For binary mode, this function is equivalent to the :class:`GzipFile`
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constructor: ``GzipFile(filename, mode, compresslevel)``. In this case, the
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*encoding*, *errors* and *newline* arguments must not be provided.
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For text mode, a :class:`GzipFile` object is created, and wrapped in an
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:class:`io.TextIOWrapper` instance with the specified encoding, error
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handling behavior, and line ending(s).
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.. versionchanged:: 3.3
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Added support for *filename* being a file object, support for text mode,
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and the *encoding*, *errors* and *newline* arguments.
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.. versionchanged:: 3.4
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Added support for the ``'x'``, ``'xb'`` and ``'xt'`` modes.
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.. versionchanged:: 3.6
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Accepts a :term:`path-like object`.
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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
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methods of a :term:`file object`, with the exception of the :meth:`truncate`
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method. At least one of *fileobj* and *filename* must be given a non-trivial
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value.
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The new class instance is based on *fileobj*, which can be a regular file, an
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:class:`io.BytesIO` 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 include 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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``'wb'``, ``'x'``, or ``'xb'``, depending on whether the file will be read or
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written. The default is the mode of *fileobj* if discernible; otherwise, the
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default is ``'rb'``.
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Note that the file is always opened in binary mode. To open a compressed file
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in text mode, use :func:`.open` (or wrap your :class:`GzipFile` with an
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:class:`io.TextIOWrapper`).
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The *compresslevel* argument is an integer from ``0`` to ``9`` controlling
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the level of compression; ``1`` is fastest and produces the least
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compression, and ``9`` is slowest and produces the most compression. ``0``
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is no 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 last modification time field in the stream when compressing. It
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should only be provided in compression mode. If omitted or ``None``, the
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current time is used. See the :attr:`mtime` attribute for more details.
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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 an :class:`io.BytesIO` object opened for
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writing as *fileobj*, and retrieve the resulting memory buffer using the
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:class:`io.BytesIO` object's :meth:`~io.BytesIO.getvalue` method.
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:class:`GzipFile` supports the :class:`io.BufferedIOBase` interface,
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including iteration and the :keyword:`with` statement. Only the
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:meth:`truncate` method isn't implemented.
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:class:`GzipFile` also provides the following method and attribute:
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.. method:: peek(n)
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Read *n* uncompressed bytes without advancing the file position.
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At most one single read on the compressed stream is done to satisfy
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the call. The number of bytes returned may be more or less than
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requested.
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.. note:: While calling :meth:`peek` does not change the file position of
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the :class:`GzipFile`, it may change the position of the underlying
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file object (e.g. if the :class:`GzipFile` was constructed with the
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*fileobj* parameter).
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.. versionadded:: 3.2
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.. attribute:: mtime
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When decompressing, the value of the last modification time field in
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the most recently read header may be read from this attribute, as an
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integer. The initial value before reading any headers is ``None``.
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All :program:`gzip` compressed streams are required to contain this
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timestamp field. Some programs, such as :program:`gunzip`\ , make use
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of the timestamp. The format is the same as the return value of
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:func:`time.time` and the :attr:`~os.stat_result.st_mtime` attribute of
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the object returned by :func:`os.stat`.
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.. versionchanged:: 3.1
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Support for the :keyword:`with` statement was added, along with the
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*mtime* constructor argument and :attr:`mtime` attribute.
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.. versionchanged:: 3.2
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Support for zero-padded and unseekable files was added.
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.. versionchanged:: 3.3
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The :meth:`io.BufferedIOBase.read1` method is now implemented.
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.. versionchanged:: 3.4
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Added support for the ``'x'`` and ``'xb'`` modes.
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.. versionchanged:: 3.5
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Added support for writing arbitrary
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:term:`bytes-like objects <bytes-like object>`.
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The :meth:`~io.BufferedIOBase.read` method now accepts an argument of
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``None``.
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.. versionchanged:: 3.6
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Accepts a :term:`path-like object`.
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.. function:: compress(data, compresslevel=9)
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Compress the *data*, returning a :class:`bytes` object containing
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the compressed data. *compresslevel* has the same meaning as in
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the :class:`GzipFile` constructor above.
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.. versionadded:: 3.2
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.. function:: decompress(data)
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Decompress the *data*, returning a :class:`bytes` object containing the
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uncompressed data.
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.. versionadded:: 3.2
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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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with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
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file_content = f.read()
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Example of how to create a compressed GZIP file::
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import gzip
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content = b"Lots of content here"
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with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
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f.write(content)
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Example of how to GZIP compress an existing file::
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import gzip
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import shutil
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with open('/home/joe/file.txt', 'rb') as f_in:
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with gzip.open('/home/joe/file.txt.gz', 'wb') as f_out:
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shutil.copyfileobj(f_in, f_out)
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Example of how to GZIP compress a binary string::
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import gzip
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s_in = b"Lots of content here"
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s_out = gzip.compress(s_in)
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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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