bz2
Gustavo Niemeyer <niemeyer@conectiva.com>
Gustavo Niemeyer <niemeyer@conectiva.com>
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.
For other archive formats, see the gzip
, zipfile
, and tarfile
modules.
Here is a summary of the features offered by the bz2 module:
BZ2File
class implements a complete file interface, including~BZ2File.readline
,~BZ2File.readlines
,~BZ2File.writelines
,~BZ2File.seek
, etc;BZ2File
class implements emulated~BZ2File.seek
support;BZ2File
class implements universal newline support;BZ2File
class offers an optimized line iteration using the readahead algorithm borrowed from file objects;- Sequential (de)compression supported by
BZ2Compressor
andBZ2Decompressor
classes; - One-shot (de)compression supported by
compress
anddecompress
functions; - Thread safety uses individual locking mechanism.
Handling of compressed files is offered by the BZ2File
class.
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 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 file
instances.
BZ2File
supports the with
statement.
2.7 Support for the with
statement was added.
close()
Close the file. Sets data attribute closed
to true. A closed file cannot be used for further I/O operations. close
may be called more than once without error.
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.
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.
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.
xreadlines()
For backward compatibility. BZ2File
objects now include the performance optimizations previously implemented in the xreadlines
module.
2.3 This exists only for compatibility with the method by this name on file
objects, which is deprecated. Use for line in file
instead.
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.
tell()
Return the current file position, an integer (may be a long integer).
write(data)
Write string data to file. Note that due to buffering, close
may be needed before the file on disk reflects the data written.
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 compression and decompression is done using the classes BZ2Compressor
and BZ2Decompressor
.
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 compress
function instead. The compresslevel parameter, if given, must be a number between 1
and 9
; the default is 9
.
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 flush
method to finish the compression process, and return what is left in internal buffers.
flush()
Finish the compression process and return what is left in internal buffers. You must not use the compressor object after calling this method.
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 decompress
function instead.
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, EOFError
will be raised. If any data was found after the end of stream, it'll be ignored and saved in unused_data
attribute.
One-shot compression and decompression is provided through the compress
and decompress
functions.
compress(data[, compresslevel])
Compress data in one shot. If you want to compress data sequentially, use an instance of BZ2Compressor
instead. The compresslevel parameter, if given, must be a number between 1
and 9
; the default is 9
.
decompress(data)
Decompress data in one shot. If you want to decompress data sequentially, use an instance of BZ2Decompressor
instead.