13.3. bz2 — 支持 bzip2 压缩 ¶

Open a bzip2-compressed file in binary mode.

若 filename 是 str or bytes object, open the named file directly. Otherwise, filename should be a 文件对象 , which will be used to read or write the compressed data.

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' .

buffering argument is ignored. Its use is deprecated.

若 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.

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.

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.

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 ).

3.3 版新增。

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 。默认为 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.

Create a new decompressor object. This object may be used to decompress data incrementally. For one-shot compression, use the decompress() function instead.

decompress ( data , max_length=-1 ) ¶

Decompress data (a 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.

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 .

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。

3.5 版改变： 添加 max_length 参数。

eof ¶

True if the end-of-stream marker has been reached.

3.3 版新增。

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 若 decompress() method can provide more decompressed data before requiring new uncompressed input.

3.5 版新增。