Python 3.6.5 Documentation >  "bz2" — Support for **bzip2** compression

"bz2" — Support for **bzip2** compression
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**Source code:** Lib/bz2.py

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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.

(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).

New in version 3.3.

Changed in version 3.4: The "'x'" (exclusive creation) mode was
added.

Changed in version 3.6: 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.

Note: 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*).

New in version 3.3.

Changed in version 3.1: Support for the "with" statement was added.

Changed in version 3.3: The "fileno()", "readable()", "seekable()",
"writable()", "read1()" and "readinto()" methods were added.

Changed in version 3.3: Support was added for *filename* being a
*file object* instead of an actual filename.

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

Changed in version 3.4: The "'x'" (exclusive creation) mode was
added.

Changed in version 3.5: The "read()" method now accepts an argument
of "None".

Changed in version 3.6: Accepts a *path-like object*.

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.

Note: 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.

Changed in version 3.5: Added the *max_length* parameter.

eof

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

New in version 3.3.

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.

New in version 3.5.

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.

Changed in version 3.3: Support for multi-stream inputs was added.