13.3. "bz2" --- Support for **bzip2** compression
*************************************************

**Source code:** Lib/bz2.py

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

This module provides a comprehensive interface for compressing and
decompressing data using the bzip2 compression algorithm.

The "bz2" module contains:

* The "open()" function and "BZ2File" class for reading and writing
  compressed files.

* The "BZ2Compressor" and "BZ2Decompressor" classes for incremental
  (de)compression.

* The "compress()" and "decompress()" functions for one-shot
  (de)compression.

All of the classes in this module may safely be accessed from multiple
threads.


13.3.1. (De)compression of files
================================

bz2.open(filename, mode='r', compresslevel=9, encoding=None, errors=None, newline=None)

   Open a bzip2-compressed file in binary or text mode, returning a
   *file object*.

   As with the constructor for "BZ2File", the *filename* argument can
   be an actual filename (a "str" or "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
   "BZ2File" constructor.

   For binary mode, this function is equivalent to the "BZ2File"
   constructor: "BZ2File(filename, mode,
   compresslevel=compresslevel)". In this case, the *encoding*,
   *errors* and *newline* arguments must not be provided.

   For text mode, a "BZ2File" object is created, and wrapped in an
   "io.TextIOWrapper" instance with the specified encoding, error
   handling behavior, and line ending(s).

   3.3 版新加入.

   3.4 版更變: The "'x'" (exclusive creation) mode was added.

   3.6 版更變: Accepts a *path-like object*.

class bz2.BZ2File(filename, mode='r', buffering=None, compresslevel=9)

   Open a bzip2-compressed file in binary mode.

   If *filename* is a "str" or "bytes" object, open the named file
   directly. Otherwise, *filename* should be a *file object*, which
   will be used to read or write the compressed data.

   The *mode* argument can be either "'r'" for reading (default),
   "'w'" for overwriting, "'x'" for exclusive creation, or "'a'" for
   appending. These can equivalently be given as "'rb'", "'wb'",
   "'xb'" 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'".

   The *buffering* argument is ignored. Its use is deprecated.

   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.

   "BZ2File" provides all of the members specified by the
   "io.BufferedIOBase", except for "detach()" and "truncate()".
   Iteration and the "with" statement are supported.

   "BZ2File" also provides the following method:

   peek([n])

      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.

      備註: While calling "peek()" does not change the file position
        of the "BZ2File", it may change the position of the underlying
        file object (e.g. if the "BZ2File" was constructed by passing
        a file object for *filename*).

      3.3 版新加入.

   3.1 版更變: Support for the "with" statement was added.

   3.3 版更變: The "fileno()", "readable()", "seekable()",
   "writable()", "read1()" and "readinto()" methods were added.

   3.3 版更變: Support was added for *filename* being a *file object*
   instead of an actual filename.

   3.3 版更變: The "'a'" (append) mode was added, along with support
   for reading multi-stream files.

   3.4 版更變: The "'x'" (exclusive creation) mode was added.

   3.5 版更變: The "read()" method now accepts an argument of "None".

   3.6 版更變: Accepts a *path-like object*.


13.3.2. Incremental (de)compression
===================================

class bz2.BZ2Compressor(compresslevel=9)

   Create a new compressor object. This object may be used to compress
   data incrementally. For one-shot compression, use the "compress()"
   function instead.

   *compresslevel*, if given, must be a number between "1" and "9".
   The default is "9".

   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 "flush()" method to finish the compression process.

   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.

class bz2.BZ2Decompressor

   Create a new decompressor object. This object may be used to
   decompress data incrementally. For one-shot compression, use the
   "decompress()" function instead.

   備註: This class does not transparently handle inputs containing
     multiple compressed streams, unlike "decompress()" and "BZ2File".
     If you need to decompress a multi-stream input with
     "BZ2Decompressor", you must use a new decompressor for each
     stream.

   decompress(data, max_length=-1)

      Decompress *data* (a *bytes-like object*), returning
      uncompressed data as bytes. Some of *data* may be buffered
      internally, for use in later calls to "decompress()". The
      returned data should be concatenated with the output of any
      previous calls to "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 "needs_input" attribute will be set
      to "False". In this case, the next call to "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 "needs_input" attribute will be
      set to "True".

      Attempting to decompress data after the end of stream is reached
      raises an *EOFError*.  Any data found after the end of the
      stream is ignored and saved in the "unused_data" attribute.

      3.5 版更變: Added the *max_length* parameter.

   eof

      "True" if the end-of-stream marker has been reached.

      3.3 版新加入.

   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''".

   needs_input

      "False" if the "decompress()" method can provide more
      decompressed data before requiring new uncompressed input.

      3.5 版新加入.


13.3.3. One-shot (de)compression
================================

bz2.compress(data, compresslevel=9)

   Compress *data*.

   *compresslevel*, if given, must be a number between "1" and "9".
   The default is "9".

   For incremental compression, use a "BZ2Compressor" instead.

bz2.decompress(data)

   Decompress *data*.

   If *data* is the concatenation of multiple compressed streams,
   decompress all of the streams.

   For incremental decompression, use a "BZ2Decompressor" instead.

   3.3 版更變: Support for multi-stream inputs was added.
