程式扎記: [Python Std Library] Data Compress/Archive : bz2 — Compression compatible with bzip2

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2012年6月3日 星期日

[Python Std Library] Data Compress/Archive : bz2 — Compression compatible with bzip2


來源自 這裡
Preface :
New in version 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. Below is a summary of the features offered by the bz2 module :
* BZ2File class implements a complete file interface, including readline()readlines()writelines()seek(), etc;
* BZ2File class implements emulated 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 and BZ2Decompressor classes;
* One-shot (de)compression supported by compress() and decompress() functions;
* Thread safety uses individual locking mechanism.

(De)compression of files :
Handling of compressed files is offered by the BZ2File class.
- class bz2.BZ2File(filename[, mode[, buffering[, compresslevel]]])
Changed in version 2.7: Support for the with statement was added.
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.

For BZ2File class, it supported below APIs :
close()
Close the file. Sets data attribute closed to true. A closed file cannot be used for further I/O operations. This API 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.

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).

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 (de)compression :
Sequential compression and decompression is done using the classes BZ2Compressor and BZ2Decompressor.

- class bz2.BZ2Compressor([compresslevel])
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.

class BZ2Compressor support below APIs :
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 theflush() 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.

- class bz2.BZ2Decompressor
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.

class BZ2Decompressor support below APIs :
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 (de)compression :
One-shot compression and decompression is provided through below functions :
bz2.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.

bz2.decompress(data)
Decompress data in one shot. If you want to decompress data sequentially, use an instance of BZ2Decompressor instead :

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