bz2
— 压缩兼容
bzip2
¶
2.3 版新增。
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.
Here is a summary of the features offered by the bz2 module:
BZ2File
class implements a complete file interface, including
readline()
,
readlines()
,
writelines()
,
seek()
，等；
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
类；
One-shot (de)compression supported by
compress()
and
decompress()
functions;
Thread safety uses individual locking mechanism.
注意
Handling of multi-stream bzip2 files is not supported. Modules such as bz2file let you overcome this.
Handling of compressed files is offered by the
BZ2File
类。
bz2.
BZ2File
(
filename
[
,
mode
[
,
buffering
[
,
compresslevel
]
]
]
)
¶
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
有给定，
0
means unbuffered, and larger numbers specify the buffer size; the default is
0
。若
compresslevel
is given, it must be a number between
1
and
9
; the default is
9
。添加
'U'
to mode to open the file for input in
通用换行符
mode. 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
实例。
2.7 版改变：
支持
with
语句被添加。
注意
This class does not support input files containing multiple streams (such as those produced by the
pbzip2
tool). When reading such an input file, only the first stream will be accessible. If you require support for multi-stream files, consider using the third-party
bz2file
module (available from
PyPI
). This module provides a backport of Python 3.3’s
BZ2File
class, which does support multi-stream files.
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
]
)
¶
读取最多 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
模块。
从 2.3 版起弃用：
This exists only for compatibility with the method by this name on
file
objects, which is deprecated. Use
for line in file
代替。
seek
(
offset
[
,
whence
]
)
¶
Move to new file position. Argument
offset
is a byte count. Optional argument
whence
默认为
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
)
¶
写入字符串
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
.
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
.
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.
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.
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
属性。
One-shot compression and decompression is provided through the
compress()
and
decompress()
函数。
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
代替。