module-site.html

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<H1><A NAME="SECTION0052300000000000000000">
3.23 <tt class="module">site</tt> --
         Site-specific configuration hook</A>
</H1>

<P>


<P>
<b>This module is automatically imported during initialization.</b>

<P>
In earlier versions of Python (up to and including 1.5a3), scripts or
modules that needed to use site-specific modules would place
"<tt class="samp">import site</tt>" somewhere near the top of their code.  This is no
longer necessary.

<P>
This will append site-specific paths to the module search path.


<P>
It starts by constructing up to four directories from a head and a
tail part.  For the head part, it uses <code>sys.prefix</code> and
<code>sys.exec_prefix</code>; empty heads are skipped.  For
the tail part, it uses the empty string (on Macintosh or Windows) or
it uses first <span class="file">lib/python2.0/site-packages</span> and then
<span class="file">lib/site-python</span> (on Unix).  For each of the distinct
head-tail combinations, it sees if it refers to an existing directory,
and if so, adds to <code>sys.path</code>, and also inspects the path for
configuration files.


<P>
A path configuration file is a file whose name has the form
<span class="file"><var>package</var>.pth</span>; its contents are additional items (one
per line) to be added to <code>sys.path</code>.  Non-existing items are
never added to <code>sys.path</code>, but no check is made that the item
refers to a directory (rather than a file).  No item is added to
<code>sys.path</code> more than once.  Blank lines and lines beginning with
<code>#</code> are skipped.


<P>
For example, suppose <code>sys.prefix</code> and <code>sys.exec_prefix</code> are
set to <span class="file">/usr/local</span>.  The Python 2.0 library is then
installed in <span class="file">/usr/local/lib/python2.0</span> (where only the
first three characters of <code>sys.version</code> are used to form the
installation path name).  Suppose this has a subdirectory
<span class="file">/usr/local/lib/python2.0/site-packages</span> with three
subsubdirectories, <span class="file">foo</span>, <span class="file">bar</span> and <span class="file">spam</span>, and two
path configuration files, <span class="file">foo.pth</span> and <span class="file">bar.pth</span>.  Assume
<span class="file">foo.pth</span> contains the following:

<P>
<dl><dd><pre class="verbatim">
# foo package configuration

foo
bar
bletch
</pre></dl>

<P>
and <span class="file">bar.pth</span> contains:

<P>
<dl><dd><pre class="verbatim">
# bar package configuration

bar
</pre></dl>

<P>
Then the following directories are added to <code>sys.path</code>, in this
order:

<P>
<dl><dd><pre class="verbatim">
/usr/local/lib/python1.5/site-packages/bar
/usr/local/lib/python1.5/site-packages/foo
</pre></dl>

<P>
Note that <span class="file">bletch</span> is omitted because it doesn't exist; the
<span class="file">bar</span> directory precedes the <span class="file">foo</span> directory because
<span class="file">bar.pth</span> comes alphabetically before <span class="file">foo.pth</span>; and
<span class="file">spam</span> is omitted because it is not mentioned in either path
configuration file.

<P>
After these path manipulations, an attempt is made to import a module
named <tt class="module">sitecustomize</tt>, which can
perform arbitrary site-specific customizations.  If this import fails
with an <tt class="exception">ImportError</tt> exception, it is silently ignored.

<P>
Note that for some non-Unix systems, <code>sys.prefix</code> and
<code>sys.exec_prefix</code> are empty, and the path manipulations are
skipped; however the import of
<tt class="module">sitecustomize</tt> is still attempted.

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