:mod:`bz2` --- Compression compatible with :program:`bzip2`

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

.. module:: bz2

   :synopsis: Interface to compression and decompression routines compatible with bzip2.

.. moduleauthor:: Gustavo Niemeyer <niemeyer@conectiva.com>

.. sectionauthor:: Gustavo Niemeyer <niemeyer@conectiva.com>

.. versionadded:: 2.3

This module provides a comprehensive interface for the bz2 compression library.

It implements a complete file interface, one-shot (de)compression functions, and

types for sequential (de)compression.

For other archive formats, see the :mod:`gzip`, :mod:`zipfile`, and

:mod:`tarfile` modules.

Here is a summary of the features offered by the bz2 module:

* :class:`BZ2File` class implements a complete file interface, including

  :meth:`readline`, :meth:`readlines`, :meth:`writelines`, :meth:`seek`, etc;

* :class:`BZ2File` class implements emulated :meth:`seek` support;

* :class:`BZ2File` class implements universal newline support;

* :class:`BZ2File` class offers an optimized line iteration using the readahead

  algorithm borrowed from file objects;

* Sequential (de)compression supported by :class:`BZ2Compressor` and

  :class:`BZ2Decompressor` classes;

* One-shot (de)compression supported by :func:`compress` and :func:`decompress`

  functions;

* Thread safety uses individual locking mechanism.

(De)compression of files

------------------------

Handling of compressed files is offered by the :class:`BZ2File` class.

.. class:: BZ2File(filename[, mode[, buffering[, compresslevel]]])

   Open a bz2 file. Mode can be either ``'r'`` or ``'w'``, for reading (default)

   or writing. When opened for writing, the file will be created if it doesn't

   exist, and truncated otherwise. If *buffering* is given, ``0`` means

   unbuffered, and larger numbers specify the buffer size; the default is

   ``0``. If *compresslevel* is given, it must be a number between ``1`` and

   ``9``; the default is ``9``. Add a ``'U'`` to mode to open the file for input

   with universal newline support. Any line ending in the input file will be

   seen as a ``'\n'`` in Python.  Also, a file so opened gains the attribute

   :attr:`newlines`; the value for this attribute is one of ``None`` (no newline

   read yet), ``'\r'``, ``'\n'``, ``'\r\n'`` or a tuple containing all the

   newline types seen. Universal newlines are available only when

   reading. Instances support iteration in the same way as normal :class:`file`

   instances.

   .. method:: close()

      Close the file. Sets data attribute :attr:`closed` to true. A closed file

      cannot be used for further I/O operations. :meth:`close` may be called

      more than once without error.

   .. method:: read([size])

      Read at most *size* uncompressed bytes, returned as a string. If the

      *size* argument is negative or omitted, read until EOF is reached.

   .. method:: readline([size])

      Return the next line from the file, as a string, retaining newline. A

      non-negative *size* argument limits the maximum number of bytes to return

      (an incomplete line may be returned then). Return an empty string at EOF.

   .. method:: readlines([size])

      Return a list of lines read. The optional *size* argument, if given, is an

      approximate bound on the total number of bytes in the lines returned.

   .. method:: xreadlines()

      For backward compatibility. :class:`BZ2File` objects now include the

      performance optimizations previously implemented in the :mod:`xreadlines`

      module.

      .. deprecated:: 2.3 

         This exists only for compatibility with the method by this name on

         :class:`file` objects, which is deprecated.  Use ``for line in file``

         instead.

   .. method:: seek(offset[, whence])

      Move to new file position. Argument *offset* is a byte count. Optional

      argument *whence* defaults to ``os.SEEK_SET`` or ``0`` (offset from start

      of file; offset should be ``>= 0``); other values are ``os.SEEK_CUR`` or

      ``1`` (move relative to current position; offset can be positive or

      negative), and ``os.SEEK_END`` or ``2`` (move relative to end of file;

      offset is usually negative, although many platforms allow seeking beyond

      the end of a file).

      Note that seeking of bz2 files is emulated, and depending on the

      parameters the operation may be extremely slow.

   .. method:: tell()

      Return the current file position, an integer (may be a long integer).

   .. method:: write(data)

      Write string *data* to file. Note that due to buffering, :meth:`close` may

      be needed before the file on disk reflects the data written.

   .. method:: writelines(sequence_of_strings)

      Write the sequence of strings to the file. Note that newlines are not

      added. The sequence can be any iterable object producing strings. This is

      equivalent to calling write() for each string.

Sequential (de)compression

--------------------------

Sequential compression and decompression is done using the classes

:class:`BZ2Compressor` and :class:`BZ2Decompressor`.

.. class:: BZ2Compressor([compresslevel])

   Create a new compressor object. This object may be used to compress data

   sequentially. If you want to compress data in one shot, use the

   :func:`compress` function instead. The *compresslevel* parameter, if given,

   must be a number between ``1`` and ``9``; the default is ``9``.

   .. method:: compress(data)

      Provide more data to the compressor object. It will return chunks of

      compressed data whenever possible. When you've finished providing data to

      compress, call the :meth:`flush` method to finish the compression process,

      and return what is left in internal buffers.

   .. method:: flush()

      Finish the compression process and return what is left in internal

      buffers. You must not use the compressor object after calling this method.

.. class:: BZ2Decompressor()

   Create a new decompressor object. This object may be used to decompress data

   sequentially. If you want to decompress data in one shot, use the

   :func:`decompress` function instead.

   .. method:: decompress(data)

      Provide more data to the decompressor object. It will return chunks of

      decompressed data whenever possible. If you try to decompress data after

      the end of stream is found, :exc:`EOFError` will be raised. If any data

      was found after the end of stream, it'll be ignored and saved in

      :attr:`unused_data` attribute.

One-shot (de)compression

------------------------

One-shot compression and decompression is provided through the :func:`compress`

and :func:`decompress` functions.

.. function:: compress(data[, compresslevel])

   Compress *data* in one shot. If you want to compress data sequentially, use

   an instance of :class:`BZ2Compressor` instead. The *compresslevel* parameter,

   if given, must be a number between ``1`` and ``9``; the default is ``9``.

.. function:: decompress(data)

   Decompress *data* in one shot. If you want to decompress data sequentially,

   use an instance of :class:`BZ2Decompressor` instead.