\section{\module{gzip} ---         Support for \program{gzip} files} \declaremodule{standard}{gzip}\modulesynopsis{Interfaces for \program{gzip} compression anddecompression using file objects.}  The data compression provided by the \code{zlib} module is compatiblewith that used by the GNU compression program \program{gzip}.Accordingly, the \module{gzip} module provides the \class{GzipFile}class to read and write \program{gzip}-format files, automaticallycompressing or decompressing the data so it looks like an ordinaryfile object.  Note that additional file formats which can bedecompressed by the \program{gzip} and \program{gunzip} programs, such as those produced by \program{compress} and \program{pack}, are notsupported by this module. The module defines the following items: \begin{classdesc}{GzipFile}{\optional{filename\optional{, mode\optional{,                            compresslevel\optional{, fileobj}}}}}Constructor for the \class{GzipFile} class, which simulates most ofthe methods of a file object, with the exception of the \method{readinto()}and \method{truncate()} methods.  At least one of\var{fileobj} and \var{filename} must be given a non-trivial value. The new class instance is based on \var{fileobj}, which can be aregular file, a \class{StringIO} object, or any other object whichsimulates a file.  It defaults to \code{None}, in which case\var{filename} is opened to provide a file object. When \var{fileobj} is not \code{None}, the \var{filename} argument isonly used to be included in the \program{gzip} file header, which mayincludes the original filename of the uncompressed file.  It defaultsto the filename of \var{fileobj}, if discernible; otherwise, itdefaults to the empty string, and in this case the original filenameis not included in the header. The \var{mode} argument can be any of \code{'r'}, \code{'rb'},\code{'a'}, \code{'ab'}, \code{'w'}, or \code{'wb'}, depending onwhether the file will be read or written.  The default is the mode of\var{fileobj} if discernible; otherwise, the default is \code{'rb'}.If not given, the 'b' flag will be added to the mode to ensure thefile is opened in binary mode for cross-platform portability. The \var{compresslevel} argument is an integer from \code{1} to\code{9} controlling the level of compression; \code{1} is fastest andproduces the least compression, and \code{9} is slowest and producesthe most compression.  The default is \code{9}. Calling a \class{GzipFile} object's \method{close()} method does notclose \var{fileobj}, since you might wish to append more materialafter the compressed data.  This also allows you to pass a\class{StringIO} object opened for writing as \var{fileobj}, andretrieve the resulting memory buffer using the \class{StringIO}object's \method{getvalue()} method.\end{classdesc} \begin{funcdesc}{open}{filename\optional{, mode\optional{, compresslevel}}}This is a shorthand for \code{GzipFile(\var{filename},}\code{\var{mode},} \code{\var{compresslevel})}.  The \var{filename}argument is required; \var{mode} defaults to \code{'rb'} and\var{compresslevel} defaults to \code{9}.\end{funcdesc} \begin{seealso}  \seemodule{zlib}{The basic data compression module needed to support                   the \program{gzip} file format.}\end{seealso}