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diff --git a/Doc/library/bz2.rst b/Doc/library/bz2.rst new file mode 100644 index 0000000000..a8c0911294 --- /dev/null +++ b/Doc/library/bz2.rst @@ -0,0 +1,181 @@ + +: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. + +Here is a resume 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; + +* Complete inline documentation; + + +(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:: BZ2File.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:: BZ2File.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:: BZ2File.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:: BZ2File.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:: BZ2File.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:: BZ2File.tell() + + Return the current file position, an integer (may be a long integer). + + +.. method:: BZ2File.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:: BZ2File.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:: BZ2Compressor.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:: BZ2Compressor.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:: BZ2Decompressor.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. + |