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:mod:`bz2` --- Support for :program:`bzip2` compression
=======================================================
.. module:: bz2
:synopsis: Interfaces for bzip2 compression and decompression.
.. moduleauthor:: Gustavo Niemeyer <niemeyer@conectiva.com>
.. moduleauthor:: Nadeem Vawda <nadeem.vawda@gmail.com>
.. sectionauthor:: Gustavo Niemeyer <niemeyer@conectiva.com>
.. sectionauthor:: Nadeem Vawda <nadeem.vawda@gmail.com>
This module provides a comprehensive interface for compressing and
decompressing data using the bzip2 compression algorithm.
For related file formats, see the :mod:`gzip`, :mod:`zipfile`, and
:mod:`tarfile` modules.
The :mod:`bz2` module contains:
* The :class:`BZ2File` class for reading and writing compressed files.
* The :class:`BZ2Compressor` and :class:`BZ2Decompressor` classes for
incremental (de)compression.
* The :func:`compress` and :func:`decompress` functions for one-shot
(de)compression.
All of the classes in this module may safely be accessed from multiple threads.
(De)compression of files
------------------------
.. class:: BZ2File(filename=None, mode='r', buffering=None, compresslevel=9, fileobj=None)
Open a bzip2-compressed file.
The :class:`BZ2File` can wrap an existing :term:`file object` (given by
*fileobj*), or operate directly on a named file (named by *filename*).
Exactly one of these two parameters should be provided.
The *mode* argument can be either ``'r'`` for reading (default), ``'w'`` for
overwriting, or ``'a'`` for appending. If *fileobj* is provided, a mode of
``'w'`` does not truncate the file, and is instead equivalent to ``'a'``.
The *buffering* argument is ignored. Its use is deprecated.
If *mode* is ``'w'`` or ``'a'``, *compresslevel* can be a number between
``1`` and ``9`` specifying the level of compression: ``1`` produces the
least compression, and ``9`` (default) produces the most compression.
If *mode* is ``'r'``, the input file may be the concatenation of multiple
compressed streams.
:class:`BZ2File` provides all of the members specified by the
:class:`io.BufferedIOBase`, except for :meth:`detach` and :meth:`truncate`.
Iteration and the :keyword:`with` statement are supported.
:class:`BZ2File` also provides the following method:
.. method:: peek([n])
Return buffered data without advancing the file position. At least one
byte of data will be returned (unless at EOF). The exact number of bytes
returned is unspecified.
.. versionadded:: 3.3
.. versionchanged:: 3.1
Support for the :keyword:`with` statement was added.
.. versionchanged:: 3.3
The :meth:`fileno`, :meth:`readable`, :meth:`seekable`, :meth:`writable`,
:meth:`read1` and :meth:`readinto` methods were added.
.. versionchanged:: 3.3
The *fileobj* argument to the constructor was added.
.. versionchanged:: 3.3
The ``'a'`` (append) mode was added, along with support for reading
multi-stream files.
Incremental (de)compression
---------------------------
.. class:: BZ2Compressor(compresslevel=9)
Create a new compressor object. This object may be used to compress data
incrementally. For one-shot compression, use the :func:`compress` function
instead.
*compresslevel*, if given, must be a number between ``1`` and ``9``. The
default is ``9``.
.. method:: compress(data)
Provide data to the compressor object. Returns a chunk of compressed data
if possible, or an empty byte string otherwise.
When you have finished providing data to the compressor, call the
:meth:`flush` method to finish the compression process.
.. method:: flush()
Finish the compression process. Returns the compressed data left in
internal buffers.
The compressor object may not be used after this method has been called.
.. class:: BZ2Decompressor()
Create a new decompressor object. This object may be used to decompress data
incrementally. For one-shot compression, use the :func:`decompress` function
instead.
.. note::
This class does not transparently handle inputs containing multiple
compressed streams, unlike :func:`decompress` and :class:`BZ2File`. If
you need to decompress a multi-stream input with :class:`BZ2Decompressor`,
you must use a new decompressor for each stream.
.. method:: decompress(data)
Provide data to the decompressor object. Returns a chunk of decompressed
data if possible, or an empty byte string otherwise.
Attempting to decompress data after the end of the current stream is
reached raises an :exc:`EOFError`. If any data is found after the end of
the stream, it is ignored and saved in the :attr:`unused_data` attribute.
.. attribute:: eof
True if the end-of-stream marker has been reached.
.. versionadded:: 3.3
.. attribute:: unused_data
Data found after the end of the compressed stream.
If this attribute is accessed before the end of the stream has been
reached, its value will be ``b''``.
One-shot (de)compression
------------------------
.. function:: compress(data, compresslevel=9)
Compress *data*.
*compresslevel*, if given, must be a number between ``1`` and ``9``. The
default is ``9``.
For incremental compression, use a :class:`BZ2Compressor` instead.
.. function:: decompress(data)
Decompress *data*.
If *data* is the concatenation of multiple compressed streams, decompress
all of the streams.
For incremental decompression, use a :class:`BZ2Decompressor` instead.
.. versionchanged:: 3.3
Support for multi-stream inputs was added.
|
