
``bz2`` --- Support for **bzip2** compression
*********************************************

This module provides a comprehensive interface for compressing and
decompressing data using the bzip2 compression algorithm.

The ``bz2`` module contains:

* The ``open()`` function and ``BZ2File`` class for reading and
  writing compressed files.

* The ``BZ2Compressor`` and ``BZ2Decompressor`` classes for
  incremental (de)compression.

* The ``compress()`` and ``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
========================

bz2.open(filename, mode='r', compresslevel=9, encoding=None, errors=None, newline=None)

   Open a bzip2-compressed file in binary or text mode, returning a
   *file object*.

   As with the constructor for ``BZ2File``, the *filename* argument
   can be an actual filename (a ``str`` or ``bytes`` object), or an
   existing file object to read from or write to.

   The *mode* argument can be any of ``'r'``, ``'rb'``, ``'w'``,
   ``'wb'``, ``'a'``, or ``'ab'`` for binary mode, or ``'rt'``,
   ``'wt'``, or ``'at'`` for text mode. The default is ``'rb'``.

   The *compresslevel* argument is an integer from 1 to 9, as for the
   ``BZ2File`` constructor.

   For binary mode, this function is equivalent to the ``BZ2File``
   constructor: ``BZ2File(filename, mode,
   compresslevel=compresslevel)``. In this case, the *encoding*,
   *errors* and *newline* arguments must not be provided.

   For text mode, a ``BZ2File`` object is created, and wrapped in an
   ``io.TextIOWrapper`` instance with the specified encoding, error
   handling behavior, and line ending(s).

   New in version 3.3.

class class bz2.BZ2File(filename, mode='r', buffering=None, compresslevel=9)

   Open a bzip2-compressed file in binary mode.

   If *filename* is a ``str`` or ``bytes`` object, open the named file
   directly. Otherwise, *filename* should be a *file object*, which
   will be used to read or write the compressed data.

   The *mode* argument can be either ``'r'`` for reading (default),
   ``'w'`` for overwriting, or ``'a'`` for appending. These can
   equivalently be given as ``'rb'``, ``'wb'``, and ``'ab'``
   respectively.

   If *filename* is a file object (rather than an actual file name), 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.

   ``BZ2File`` provides all of the members specified by the
   ``io.BufferedIOBase``, except for ``detach()`` and ``truncate()``.
   Iteration and the ``with`` statement are supported.

   ``BZ2File`` also provides the following 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.

      New in version 3.3.

   Changed in version 3.1: Support for the ``with`` statement was
   added.

   Changed in version 3.3: The ``fileno()``, ``readable()``,
   ``seekable()``, ``writable()``, ``read1()`` and ``readinto()``
   methods were added.

   Changed in version 3.3: Support was added for *filename* being a
   *file object* instead of an actual filename.

   Changed in version 3.3: The ``'a'`` (append) mode was added, along
   with support for reading multi-stream files.


Incremental (de)compression
===========================

class class bz2.BZ2Compressor(compresslevel=9)

   Create a new compressor object. This object may be used to compress
   data incrementally. For one-shot compression, use the
   ``compress()`` function instead.

   *compresslevel*, if given, must be a number between ``1`` and
   ``9``. The default is ``9``.

   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 ``flush()`` method to finish the compression process.

   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 class bz2.BZ2Decompressor

   Create a new decompressor object. This object may be used to
   decompress data incrementally. For one-shot compression, use the
   ``decompress()`` function instead.

   Note: This class does not transparently handle inputs containing
     multiple compressed streams, unlike ``decompress()`` and
     ``BZ2File``. If you need to decompress a multi-stream input with
     ``BZ2Decompressor``, you must use a new decompressor for each
     stream.

   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 ``EOFError``. If any data is found
      after the end of the stream, it is ignored and saved in the
      ``unused_data`` attribute.

   eof

      True if the end-of-stream marker has been reached.

      New in version 3.3.

   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
========================

bz2.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 ``BZ2Compressor`` instead.

bz2.decompress(data)

   Decompress *data*.

   If *data* is the concatenation of multiple compressed streams,
   decompress all of the streams.

   For incremental decompression, use a ``BZ2Decompressor`` instead.

   Changed in version 3.3: Support for multi-stream inputs was added.
