Source code:
———
This module provides a comprehensive interface for compressing and decompressing data using the bzip2 compression algorithm.
The bz2 module contains:
The
function and
class for reading and writing compressed files.
The
and
classes for incremental (de)compression.
The
and
functions for one-shot (de)compression.
This is an
. If it is missing from your copy of CPython, look for documentation from your distributor (that is, whoever provided Python to you). If you are the distributor, see
Requirements for optional modules
.
(De)compression of files
bz2.open(filename, mode='rb', compresslevel=9, encoding=None, errors=None, newline=None)
Open a bzip2-compressed file in binary or text mode, returning a
.
As with the constructor for
, the filename argument can be an actual filename (a
or
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
constructor.
For binary mode, this function is equivalent to the
constructor: BZ2File(filename,mode,compresslevel=compresslevel). In this case, the encoding, errors and newline arguments must not be provided.
For text mode, a
object is created, and wrapped in an
instance with the specified encoding, error handling behavior, and line ending(s).
Added in version 3.3.
Changed in version 3.4: The 'x' (exclusive creation) mode was added.
classbz2.BZ2File(filename, mode='r', *, compresslevel=9)
Open a bzip2-compressed file in binary mode.
If filename is a
or
object, open the named file directly. Otherwise, filename should be a
, 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'.
If mode is 'w' or 'a', compresslevel can be an integer 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
, except for
and
. Iteration and the
statement are supported.
BZ2File also provides the following methods and attributes:
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).
Added in version 3.3.
fileno()
Return the file descriptor for the underlying file.
Added in version 3.3.
readable()
Return whether the file was opened for reading.
Added in version 3.3.
seekable()
Return whether the file supports seeking.
Added in version 3.3.
writable()
Return whether the file was opened for writing.
Added in version 3.3.
read1(size=-1)
Read up to size uncompressed bytes, while trying to avoid making multiple reads from the underlying stream. Reads up to a buffer’s worth of data if size is negative.
Returns b'' if the file is at EOF.
Added in version 3.3.
readinto(b)
Read bytes into b.
Returns the number of bytes read (0 for EOF).
Added in version 3.3.
mode
'rb' for reading and 'wb' for writing.
Added in version 3.13.
name
The bzip2 file name. Equivalent to the
attribute of the underlying
.
Added in version 3.13.
Changed in version 3.1: Support for the
statement was added.
Changed in version 3.3: Support was added for filename being a
instead of an actual filename.
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
method now accepts an argument of None.
Changed in version 3.9: The buffering parameter has been removed. It was ignored and deprecated since Python 3.0. Pass an open file object to control how the file is opened.
The compresslevel parameter became keyword-only.
Changed in version 3.10: This class is thread unsafe in the face of multiple simultaneous readers or writers, just like its equivalent classes in
and
have always been.
Incremental (de)compression
classbz2.BZ2Compressor(compresslevel=9)
Create a new compressor object. This object may be used to compress data incrementally. For one-shot compression, use the
function instead.
compresslevel, if given, must be an integer 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
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.
classbz2.BZ2Decompressor
Create a new decompressor object. This object may be used to decompress data incrementally. For one-shot compression, use the
function instead.
Note
This class does not transparently handle inputs containing multiple compressed streams, unlike
and
. 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
), 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
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
attribute will be set to True.
Attempting to decompress data after the end of stream is reached raises an
. Any data found after the end of the stream is ignored and saved in the
attribute.
Changed in version 3.5: Added the max_length parameter.
eof
True if the end-of-stream marker has been reached.
Added 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
method can provide more decompressed data before requiring new uncompressed input.
Added in version 3.5.
One-shot (de)compression
bz2.compress(data, compresslevel=9)
Compress data, a
.
compresslevel, if given, must be an integer between 1 and 9. The default is 9.
For incremental compression, use a
instead.
bz2.decompress(data)
Decompress data, a
.
If data is the concatenation of multiple compressed streams, decompress all of the streams.
For incremental decompression, use a
instead.
Changed in version 3.3: Support for multi-stream inputs was added.
Examples of usage
Below are some examples of typical usage of the bz2 module.
Using
and
to demonstrate round-trip compression:
>>> importbz2>>> data=b"""\... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum.""">>> c=bz2.compress(data)>>> len(data)/len(c)# Data compression ratio1.513595166163142>>> d=bz2.decompress(c)>>> data==d# Check equality to original object after round-tripTrueUsing
for incremental compression:
>>> importbz2>>> defgen_data(chunks=10,chunksize=1000):... """Yield incremental blocks of chunksize bytes."""... for_inrange(chunks):... yieldb"z"*chunksize...>>> comp=bz2.BZ2Compressor()>>> out=b"">>> forchunkingen_data():... # Provide data to the compressor object... out=out+comp.compress(chunk)...>>> # Finish the compression process. Call this once you have>>> # finished providing data to the compressor.>>> out=out+comp.flush()The example above uses a very “nonrandom” stream of data (a stream of b"z" chunks). Random data tends to compress poorly, while ordered, repetitive data usually yields a high compression ratio.
Writing and reading a bzip2-compressed file in binary mode:
>>> importbz2>>> data=b"""\... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum.""">>> withbz2.open("myfile.bz2","wb")asf:... # Write compressed data to file... unused=f.write(data)...>>> withbz2.open("myfile.bz2","rb")asf:... # Decompress data from file... content=f.read()...>>> content==data# Check equality to original object after round-tripTrue