: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:
- The :func:`.open` function and :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.
.. 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`.
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
.. 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.
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")