程式扎記: [Python Std Library] Data Compress/Archive : gzip — Support for gzip files

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2012年6月3日 星期日

[Python Std Library] Data Compress/Archive : gzip — Support for gzip files


來源自 這裡
Preface :
This module provides a simple interface to compress and decompress files just like the GNU programs gzip and gunzip would. The data compression is provided by thezlib module. This module provides the GzipFile class which is modeled after Python’s File Object. The GzipFile class reads and writes gzip-format files, automatically compressing or decompressing the data so that it looks like an ordinary file object.

Note that additional file formats which can be decompressed by the gzip and gunzip programs, such as those produced by compress and pack, are not supported by this module. The module defines the following items :
- class gzip.GzipFile([filename[, mode[, compresslevel[, fileobj[, mtime]]]]])
Changed in version 2.7: Support for the with statement was added.
Changed in version 2.7: Support for zero-padded files was added.

Constructor for the GzipFile class, which simulates most of the methods of a file object, with the exception of the readinto() and truncate() methods. At least one offileobj and filename must be given a non-trivial value.

The new class instance is based on fileobj, which can be a regular file, a StringIO object, or any other object which simulates a file. It defaults to None, in which case filename is opened to provide a file object.

When fileobj is not None, the filename argument is only used to be included in the gzip file header, which may includes the original filename of the uncompressed file. It defaults to the filename of fileobj, if discernible; otherwise, it defaults to the empty string, and in this case the original filename is not included in the header.

The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', or 'wb', depending on whether the file will be read or written. The default is the mode of fileobj if discernible; otherwise, the default is 'rb'. If not given, the ‘b’ flag will be added to the mode to ensure the file is opened in binary mode for cross-platform portability.

The compresslevel argument is an integer from 1 to 9 controlling the level of compression; 1 is fastest and produces the least compression, and 9 is slowest and produces the most compression. The default is 9.

The mtime argument is an optional numeric timestamp to be written to the stream when compressing. All gzip compressed streams are required to contain a timestamp. If omitted or None, the current time is used. This module ignores the timestamp when decompressing; however, some programs, such as gunzip, make use of it. The format of the timestamp is the same as that of the return value of time.time() and of the st_mtime attribute of the object returned by os.stat().

Calling a GzipFile object’s close() method does not close fileobj, since you might wish to append more material after the compressed data. This also allows you to pass a StringIO object opened for writing as fileobj, and retrieve the resulting memory buffer using the StringIO object’s getvalue() method.

GzipFile supports iteration and the with statement.

gzip.open(filename[, mode[, compresslevel]])
This is a shorthand for GzipFile(filename, mode, compresslevel). The filename argument is required; mode defaults to 'rb' and compresslevel defaults to 9.

Examples of usage :
- Example of how to read a compressed file
  1. import gzip  
  2. f = gzip.open('/home/joe/file.txt.gz''rb')  
  3. file_content = f.read()  
  4. f.close()  
- Example of how to create a compressed GZIP file
  1. import gzip  
  2. content = "Lots of content here"  
  3. f = gzip.open('/home/joe/file.txt.gz''wb')  
  4. f.write(content)  
  5. f.close()  
- Example of how to GZIP compress an existing file
  1. import gzip  
  2. f_in = open('/home/joe/file.txt''rb')  
  3. f_out = gzip.open('/home/joe/file.txt.gz''wb')  
  4. f_out.writelines(f_in)  
  5. f_out.close()  
  6. f_in.close()  
- Example of read/write compressed file :
>>> import gzip
>>> content = "Lots of content here"
>>> f = gzip.open('./test.txt.gz', 'wb')
>>> f.write(content)
20
>>> f.close()
>>> f = gzip.open('./test.txt.gz', 'rb')
>>> f.read()
'Lots of content here'
>>> f.close()

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