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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:

(De)compression of files

.. function:: open(filename, mode='rb', 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.

   .. versionchanged:: 3.6
      Accepts a :term:`path-like object`.

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 an integer 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 :exc:`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*, a :term:`bytes-like object <bytes-like object>`.

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

   For incremental compression, use a :class:`BZ2Compressor` instead.



.. function:: decompress(data)

   Decompress *data*, a :term:`bytes-like object <bytes-like object>`.

   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.

Examples of usage

Below are some examples of typical usage of the :mod:`bz2` module.

Using :func:`compress` and :func:`decompress` to demonstrate round-trip compression:

>>> import bz2
>>> data = b"""\
... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
>>> c = bz2.compress(data)
>>> len(data) / len(c)  # Data compression ratio
1.513595166163142
>>> d = bz2.decompress(c)
>>> data == d  # Check equality to original object after round-trip
True

Using :class:`BZ2Compressor` for incremental compression:

>>> import bz2
>>> def gen_data(chunks=10, chunksize=1000):
...     """Yield incremental blocks of chunksize bytes."""
...     for _ in range(chunks):
...         yield b"z" * chunksize
...
>>> comp = bz2.BZ2Compressor()
>>> out = b""
>>> for chunk in gen_data():
...     # Provide data to the compressor object
...     out = out + comp.compress(chunk)
...
>>> # Finish the compression process.  Call this once you have
>>> # finished providing data to the compressor.
>>> out = out + comp.flush()

The example above uses a very "nonrandom" stream of data (a stream of b"z" chunks). Random data tends to compress poorly, while ordered, repetitive data usually yields a high compression ratio.

Writing and reading a bzip2-compressed file in binary mode:

>>> import bz2
>>> data = b"""\
... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
>>> with bz2.open("myfile.bz2", "wb") as f:
...     # Write compressed data to file
...     unused = f.write(data)
>>> with bz2.open("myfile.bz2", "rb") as f:
...     # Decompress data from file
...     content = f.read()
>>> content == data  # Check equality to original object after round-trip
True
.. testcleanup::

   import os
   os.remove("myfile.bz2")