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<H1><A NAME="SECTION0091500000000000000000">
7.15 <tt class="module">gzip</tt> --
Support for <b class="program">gzip</b> files</A>
</H1>
<P>
<P>
The data compression provided by the <code>zlib</code> module is compatible
with that used by the GNU compression program <b class="program">gzip</b>.
Accordingly, the <tt class="module">gzip</tt> module provides the <tt class="class">GzipFile</tt>
class to read and write <b class="program">gzip</b>-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 <b class="program">gzip</b> and <b class="program">gunzip</b> programs, such
as those produced by <b class="program">compress</b> and <b class="program">pack</b>, are not
supported by this module.
<P>
The module defines the following items:
<P>
<dl><dt><b><a name='l2h-1753'><tt class='class'>GzipFile</tt></a></b> (<big>[</big><var>filename</var><big>[</big><var>, mode</var><big>[</big><var>,
compresslevel</var><big>[</big><var>, fileobj</var><big>]</big><big>]</big><big>]</big><big>]</big>)
<dd>
Constructor for the <tt class="class">GzipFile</tt> class, which simulates most of
the methods of a file object, with the exception of the
<tt class="method">seek()</tt> and <tt class="method">tell()</tt> methods. At least one of
<var>fileobj</var> and <var>filename</var> must be given a non-trivial value.
<P>
The new class instance is based on <var>fileobj</var>, which can be a
regular file, a <tt class="class">StringIO</tt> object, or any other object which
simulates a file. It defaults to <code>None</code>, in which case
<var>filename</var> is opened to provide a file object.
<P>
When <var>fileobj</var> is not <code>None</code>, the <var>filename</var> argument is
only used to be included in the <b class="program">gzip</b> file header, which may
includes the original filename of the uncompressed file. It defaults
to the filename of <var>fileobj</var>, if discernible; otherwise, it
defaults to the empty string, and in this case the original filename
is not included in the header.
<P>
The <var>mode</var> argument can be any of <code>'r'</code>, <code>'rb'</code>,
<code>'a'</code>, <code>'ab'</code>, <code>'w'</code>, or <code>'wb'</code>, depending on
whether the file will be read or written. The default is the mode of
<var>fileobj</var> if discernible; otherwise, the default is <code>'rb'</code>.
Be aware that only the <code>'rb'</code>, <code>'ab'</code>, and <code>'wb'</code>
values should be used for cross-platform portability.
<P>
The <var>compresslevel</var> argument is an integer from <code>1</code> to
<code>9</code> controlling the level of compression; <code>1</code> is fastest and
produces the least compression, and <code>9</code> is slowest and produces
the most compression. The default is <code>9</code>.
<P>
Calling a <tt class="class">GzipFile</tt> object's <tt class="method">close()</tt> method does not
close <var>fileobj</var>, since you might wish to append more material
after the compressed data. This also allows you to pass a
<tt class="class">StringIO</tt> object opened for writing as <var>fileobj</var>, and
retrieve the resulting memory buffer using the <tt class="class">StringIO</tt>
object's <tt class="method">getvalue()</tt> method.
</dl>
<P>
<dl><dt><b><a name='l2h-1754'><tt class='function'>open</tt></a></b> (<var>filename</var><big>[</big><var>, mode</var><big>[</big><var>, compresslevel</var><big>]</big><big>]</big>)
<dd>
This is a shorthand for <code>GzipFile(<var>filename</var>,</code>
<code><var>mode</var>,</code> <code><var>compresslevel</var>)</code>. The <var>filename</var>
argument is required; <var>mode</var> defaults to <code>'rb'</code> and
<var>compresslevel</var> defaults to <code>9</code>.
</dl>
<P>
<div class='seealso'>
<p class='heading'><b>See Also:</b></p>
<dl compact class="seemodule">
<dt>Module <b><tt class='module'><a href="module-zlib.html" tppabs="http://www.python.org/doc/current/lib/module-zlib.html">zlib</a></tt>:</b>
<dd>the basic data compression module.
</dl>
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