The data compression provided by the zlib module is compatible
with that used by the GNU compression program gzip.
Accordingly, the gzip module provides the GzipFile
class to read and write gzip-format files, automatically
compressing or decompressing the data so 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.
Constructor for the GzipFile class, which simulates most of
the methods of a file object, with the exception of the readinto(),
truncate(), and xreadlines() methods. At least one of
fileobj 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'.
Be aware that only the 'rb', 'ab', and 'wb'
values should be used 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.
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.