bz2
gzip — 支持 gzip 文件
gzip
源代码： Lib/bz2.py
This module provides a comprehensive interface for compressing and decompressing data using the bzip2 compression algorithm.
The bz2 module contains:
The open() 函数和 BZ2File class for reading and writing compressed files.
open()
BZ2File
The BZ2Compressor and BZ2Decompressor classes for incremental (de)compression.
BZ2Compressor
BZ2Decompressor
The compress() and decompress() functions for one-shot (de)compression.
compress()
decompress()
Open a bzip2-compressed file in binary or text mode, returning a 文件对象 .
As with the constructor for BZ2File ， filename argument can be an actual filename (a str or bytes object), or an existing file object to read from or write to.
str
bytes
The mode argument can be any of 'r' , 'rb' , 'w' , 'wb' , 'x' , 'xb' , 'a' or 'ab' 对于二进制模式，或 'rt' , 'wt' , 'xt' ，或 'at' for text mode. The default is 'rb' .
'r'
'rb'
'w'
'wb'
'x'
'xb'
'a'
'ab'
'rt'
'wt'
'xt'
'at'
The compresslevel argument is an integer from 1 to 9, as for the BZ2File 构造函数。
For binary mode, this function is equivalent to the BZ2File 构造函数： BZ2File(filename, mode, compresslevel=compresslevel) 。在此情况下， encoding , errors and newline arguments must not be provided.
BZ2File(filename, mode, compresslevel=compresslevel)
对于文本模式， BZ2File object is created, and wrapped in an io.TextIOWrapper instance with the specified encoding, error handling behavior, and line ending(s).
io.TextIOWrapper
Added in version 3.3.
3.4 版改变： The 'x' (exclusive creation) mode was added.
3.6 版改变： 接受 像路径对象 .
Open a bzip2-compressed file in binary mode.
若 filename 是 str or bytes object, open the named file directly. Otherwise, filename 应该为 文件对象 , 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' 分别。
若 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' .
若 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.
1
9
若 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.
io.BufferedIOBase
detach()
truncate()
with
BZ2File also provides the following methods:
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.
注意
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 ).
peek()
Return the file descriptor for the underlying file.
Return whether the file was opened for reading.
Return whether the file supports seeking.
Return whether the file was opened for writing.
读取直到 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.
返回 b'' if the file is at EOF.
b''
Read bytes into b .
Returns the number of bytes read (0 for EOF).
3.1 版改变： 支持 with 语句被添加。
3.3 版改变： Support was added for filename being a 文件对象 instead of an actual filename.
The 'a' (append) mode was added, along with support for reading multi-stream files.
3.5 版改变： The read() method now accepts an argument of None .
read()
None
3.9 版改变： 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.
3.10 版改变： This class is thread unsafe in the face of multiple simultaneous readers or writers, just like its equivalent classes in gzip and lzma have always been.
lzma
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 an integer between 1 and 9 。默认为 9 .
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.
Create a new decompressor object. This object may be used to decompress data incrementally. For one-shot compression, use the decompress() function instead.
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 ( 像字节对象 ), 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() .
若 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.
needs_input
False
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 .
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 属性。
EOFError
unused_data
3.5 版改变： 添加 max_length 参数。
True if the end-of-stream marker has been reached.
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'' .
False 若 decompress() method can provide more decompressed data before requiring new uncompressed input.
Added in version 3.5.
Compress data ， 像字节对象 .
For incremental compression, use a BZ2Compressor 代替。
Decompress data ， 像字节对象 .
若 data is the concatenation of multiple compressed streams, decompress all of the streams.
For incremental decompression, use a BZ2Decompressor 代替。
3.3 版改变： Support for multi-stream inputs was added.
Below are some examples of typical usage of the bz2 模块。
使用 compress() and decompress() to demonstrate round-trip compression:
>>> import bz2 >>> 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 ratio 1.513595166163142 >>> d = bz2.decompress(c) >>> data == d # Check equality to original object after round-trip True
使用 BZ2Compressor for incremental compression:
>>> import bz2 >>> def gen_data(chunks=10, chunksize=1000): ... """Yield incremental blocks of chunksize bytes.""" ... for _ in range(chunks): ... yield b"z" * chunksize ... >>> comp = bz2.BZ2Compressor() >>> out = b"" >>> for chunk in gen_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.
b"z"
Writing and reading a bzip2-compressed file in binary mode:
>>> import bz2 >>> 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.""" >>> with bz2.open("myfile.bz2", "wb") as f: ... # Write compressed data to file ... unused = f.write(data) ... >>> with bz2.open("myfile.bz2", "rb") as f: ... # Decompress data from file ... content = f.read() ... >>> content == data # Check equality to original object after round-trip True
lzma — 压缩使用 LZMA 算法
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