\section{Built-in Module \sectcode{gzip}}

\label{module-gzip}

\bimodindex{gzip}

The data compression provided by the \code{zlib} module is compatible

with that used by the GNU compression program \file{gzip}.

Accordingly, the \code{gzip} module provides the \code{GzipFile} class

to read and write \file{gzip}-format files, automatically compressing

or decompressing the data so it looks like an ordinary file object.

\code{GzipFile} objects simulate most of the methods of a file

object, though it's not possible to use the \code{seek()} and

\code{tell()} methods to access the file randomly.

\renewcommand{\indexsubitem}{(in module gzip)}

\begin{funcdesc}{open}{fileobj\optional{\, filename\optional{\, mode\, compresslevel}}}

Returns a new \code{GzipFile} object on top of \var{fileobj}, which

can be a regular file, a \code{StringIO} object, or any object which

simulates a file.

The \file{gzip} file format includes the original filename of the

uncompressed file; when opening a \code{GzipFile} object for

writing, it can be set by the \var{filename} argument. The default

value is \code{"GzippedFile"}.

\var{mode} can be either \code{'r'} or \code{'w'} depending on

whether the file will be read or written. \var{compresslevel} 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 value of

\var{compresslevel} is 9.

Calling a \code{GzipFile} object's \code{close()} method does not

close \var{fileobj}, since you might wish to append more material

after the compressed data. This also allows you to pass a

\code{StringIO} object opened for writing as \var{fileobj}, and

retrieve the resulting memory buffer using the \code{StringIO}

object's \code{getvalue()} method.

\end{funcdesc}

\begin{seealso}

\seemodule{zlib}{the basic data compression module}

\end{seealso}