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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>

Source code: :source:`Lib/bz2.py`

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

The :mod:`bz2` module contains:

All of the classes in this module may safely be accessed from multiple threads.

(De)compression of files

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

   Open a bzip2-compressed file in binary or text mode, returning a :term:`file
   object`.

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

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

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

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

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

   .. versionadded:: 3.3

   .. versionchanged:: 3.4
      The ``'x'`` (exclusive creation) mode was added.

Open a bzip2-compressed file in binary mode.

If filename is a :class:`str` or :class:`bytes` object, open the named file directly. Otherwise, filename should be a :term:`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, 'x' for exclusive creation, or 'a' for appending. These can equivalently be given as 'rb', 'wb', 'xb' 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.

: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.

   .. note:: While calling :meth:`peek` does not change the file position of
      the :class:`BZ2File`, it may change the position of the underlying file
      object (e.g. if the :class:`BZ2File` was constructed by passing a file
      object for *filename*).

   .. 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
   Support was added for *filename* being a :term:`file object` instead of an
   actual filename.


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


.. versionchanged:: 3.4
   The ``'x'`` (exclusive creation) mode was added.


.. versionchanged:: 3.5
   The :meth:`~io.BufferedIOBase.read` method now accepts an argument of
   ``None``.

Incremental (de)compression

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.

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, max_length=-1)

   Decompress *data* (a :term:`bytes-like object`), returning
   uncompressed data as bytes. Some of *data* may be buffered
   internally, for use in later calls to :meth:`decompress`. The
   returned data should be concatenated with the output of any
   previous calls to :meth:`decompress`.

   If *max_length* is nonnegative, returns at most *max_length*
   bytes of decompressed data. If this limit is reached and further
   output can be produced, the :attr:`~.needs_input` attribute will
   be set to ``False``. In this case, the next call to
   :meth:`~.decompress` may provide *data* as ``b''`` to obtain
   more of the output.

   If all of the input data was decompressed and returned (either
   because this was less than *max_length* bytes, or because
   *max_length* was negative), the :attr:`~.needs_input` attribute
   will be set to ``True``.

   Attempting to decompress data after the end of stream is reached
   raises an `EOFError`.  Any data found after the end of the
   stream is ignored and saved in the :attr:`~.unused_data` attribute.

   .. versionchanged:: 3.5
      Added the *max_length* parameter.


.. 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''``.


.. attribute:: needs_input

   ``False`` if the :meth:`.decompress` method can provide more
   decompressed data before requiring new uncompressed input.

   .. versionadded:: 3.5

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.