13.3. bz2 — Support for bzip2 compression

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', 'a', or 'ab' for binary mode, or 'rt', 'wt', 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.

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, 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'.

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.

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.

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)

Provide data to the decompressor object. Returns a chunk of decompressed data if possible, or an empty byte string otherwise.

Attempting to decompress data after the end of the current stream is reached raises an EOFError. If any data is found after the end of the stream, it is ignored and saved in the unused_data attribute.

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''.

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.

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