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diff --git a/Doc/library/bz2.rst b/Doc/library/bz2.rst index 93144b6..d06a39a 100644 --- a/Doc/library/bz2.rst +++ b/Doc/library/bz2.rst @@ -1,201 +1,202 @@ -:mod:`bz2` --- Compression compatible with :program:`bzip2` -=========================================================== +:mod:`bz2` --- Support for :program:`bzip2` compression +======================================================= .. module:: bz2 - :synopsis: Interface to compression and decompression routines - compatible with bzip2. + :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> -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. +This module provides a comprehensive interface for compressing and +decompressing data using the bzip2 compression algorithm. -Here is a summary of the features offered by the bz2 module: +The :mod:`bz2` module contains: -* :class:`BZ2File` class implements a complete file interface, including - :meth:`~BZ2File.readline`, :meth:`~BZ2File.readlines`, - :meth:`~BZ2File.writelines`, :meth:`~BZ2File.seek`, etc; +* 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. -* :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 a readahead - algorithm; - -* 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. +All of the classes in this module may safely be accessed from multiple threads. (De)compression of files ------------------------ -Handling of compressed files is offered by the :class:`BZ2File` class. +.. 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`. -.. index:: - single: universal newlines; bz2.BZ2File class + 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. -.. class:: BZ2File(filename, mode='r', buffering=0, compresslevel=9) + The *mode* argument can be any of ``'r'``, ``'rb'``, ``'w'``, ``'wb'``, + ``'a'``, or ``'ab'`` for binary mode, or ``'rt'``, ``'wt'``, or ``'at'`` for + text mode. The default is ``'rb'``. - 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 - in :term:`universal newlines` mode. 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. + The *compresslevel* argument is an integer from 1 to 9, as for the + :class:`BZ2File` constructor. - :class:`BZ2File` supports the :keyword:`with` statement. + 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. - .. versionchanged:: 3.1 - Support for the :keyword:`with` statement was added. + 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 - .. 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. +.. class:: BZ2File(filename, mode='r', buffering=None, compresslevel=9) + Open a bzip2-compressed file in binary mode. - .. method:: close() + 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. - 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. + The *mode* argument can be either ``'r'`` for reading (default), ``'w'`` for + overwriting, or ``'a'`` for appending. These can equivalently be given as + ``'rb'``, ``'wb'``, 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'``. - .. method:: read([size]) + The *buffering* argument is ignored. Its use is deprecated. - Read at most *size* uncompressed bytes, returned as a byte string. If the - *size* argument is negative or omitted, read until EOF is reached. + 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. - .. method:: readline([size]) + :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. - Return the next line from the file, as a byte 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 byte - string at EOF. + :class:`BZ2File` also provides the following method: + .. method:: peek([n]) - .. method:: readlines([size]) + 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. - 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. + .. versionadded:: 3.3 + .. versionchanged:: 3.1 + Support for the :keyword:`with` statement was added. - .. method:: seek(offset[, whence]) + .. versionchanged:: 3.3 + The :meth:`fileno`, :meth:`readable`, :meth:`seekable`, :meth:`writable`, + :meth:`read1` and :meth:`readinto` methods were added. - 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). + .. versionchanged:: 3.3 + Support was added for *filename* being a :term:`file object` instead of an + actual filename. - Note that seeking of bz2 files is emulated, and depending on the - parameters the operation may be extremely slow. + .. versionchanged:: 3.3 + The ``'a'`` (append) mode was added, along with support for reading + multi-stream files. - .. method:: tell() +Incremental (de)compression +--------------------------- - Return the current file position, an integer. +.. class:: BZ2Compressor(compresslevel=9) + Create a new compressor object. This object may be used to compress data + incrementally. For one-shot compression, use the :func:`compress` function + instead. - .. method:: write(data) + *compresslevel*, if given, must be a number between ``1`` and ``9``. The + default is ``9``. - Write the byte string *data* to file. Note that due to buffering, - :meth:`close` may be needed before the file on disk reflects the data - written. + .. method:: compress(data) + Provide data to the compressor object. Returns a chunk of compressed data + if possible, or an empty byte string otherwise. - .. method:: writelines(sequence_of_byte_strings) + When you have finished providing data to the compressor, call the + :meth:`flush` method to finish the compression process. - Write the sequence of byte strings to the file. Note that newlines are not - added. The sequence can be any iterable object producing byte strings. - This is equivalent to calling write() for each byte string. + .. method:: flush() -Sequential (de)compression --------------------------- + Finish the compression process. Returns the compressed data left in + internal buffers. -Sequential compression and decompression is done using the classes -:class:`BZ2Compressor` and :class:`BZ2Decompressor`. + The compressor object may not be used after this method has been called. -.. class:: BZ2Compressor(compresslevel=9) +.. class:: BZ2Decompressor() - 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``. + Create a new decompressor object. This object may be used to decompress data + incrementally. For one-shot compression, use the :func:`decompress` function + instead. - .. method:: compress(data) + .. 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. - 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:: decompress(data) + Provide data to the decompressor object. Returns a chunk of decompressed + data if possible, or an empty byte string otherwise. - .. method:: flush() + Attempting to decompress data after the end of the current stream is + reached raises an :exc:`EOFError`. If any data is found after the end of + the stream, it is ignored and saved in the :attr:`unused_data` attribute. - Finish the compression process and return what is left in internal - buffers. You must not use the compressor object after calling this method. + .. attribute:: eof -.. class:: BZ2Decompressor() + True if the end-of-stream marker has been reached. - 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. + .. versionadded:: 3.3 - .. 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. + .. 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''``. One-shot (de)compression ------------------------ -One-shot compression and decompression is provided through the :func:`compress` -and :func:`decompress` functions. +.. function:: compress(data, compresslevel=9) + Compress *data*. -.. function:: compress(data, compresslevel=9) + *compresslevel*, if given, must be a number between ``1`` and ``9``. The + default is ``9``. - 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``. + For incremental compression, use a :class:`BZ2Compressor` instead. .. function:: decompress(data) - Decompress *data* in one shot. If you want to decompress data sequentially, - use an instance of :class:`BZ2Decompressor` instead. + 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. |