mirror of https://github.com/python/cpython
216 lines
7.8 KiB
ReStructuredText
216 lines
7.8 KiB
ReStructuredText
|
|
: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:`~BZ2File.readline`, :meth:`~BZ2File.readlines`,
|
|
:meth:`~BZ2File.writelines`, :meth:`~BZ2File.seek`, etc;
|
|
|
|
* :class:`BZ2File` class implements emulated :meth:`~BZ2File.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.
|
|
|
|
:class:`BZ2File` supports the :keyword:`with` statement.
|
|
|
|
.. versionchanged:: 2.7
|
|
Support for the :keyword:`with` statement was added.
|
|
|
|
|
|
.. note::
|
|
|
|
This class does not support input files containing multiple streams (such
|
|
as those produced by the :program:`pbzip2` tool). When reading such an
|
|
input file, only the first stream will be accessible. If you require
|
|
support for multi-stream files, consider using the third-party
|
|
:mod:`bz2file` module (available from
|
|
`PyPI <http://pypi.python.org/pypi/bz2file>`_). This module provides a
|
|
backport of Python 3.3's :class:`BZ2File` class, which does support
|
|
multi-stream files.
|
|
|
|
|
|
.. 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.
|
|
|