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<H1><A NAME="SECTION008500000000000000000"></A><A NAME="ssi-conditionals"></A>
<BR>
6.5 Conditional Expressions
</H1>
<P>
SSI allows for some programmability in its own right through the use of
conditional expressions. The structure of this conditional construct is:
<P>
<div class="verbatim"><pre>
<!--#if expr="test_condition" -->
<!--#elif expr="test_condition" -->
<!--#else -->
<!--#endif -->
</pre></div>
<P>
A test condition can be any sort of logical comparison, either comparing
values to one another, or testing the 'truth' of a particular value.
<P>
The source of variables used in conditional expressions is distinct from
the set of global data used by the Python code executed within a page.
Instead, the variables are sourced from the <code>subprocess_env</code> table
object contained within the request object. The values of these variables
can be set from within a page using the SSI 'set' directive, or by a range
of other Apache directives within the Apache configuration files such as
<code>BrowserMatchNoCase</code> and <code>SetEnvIf</code>.
<P>
To set these variables from within a mod_python handler, the
<code>subprocess_env</code> table object would be manipulated directly through
the request object.
<P>
<div class="verbatim"><pre>
from mod_python import apache
def fixuphandler(req):
debug = req.get_config().get('PythonDebug', '0')
req.subprocess_env['DEBUG'] = debug
return apache.OK
</pre></div>
<P>
If being done from within Python code contained within the page itself, the
request object would first have to be accessed via the filter object.
<P>
<div class="verbatim"><pre>
<!--#python exec="
debug = filter.req.get_config().get('PythonDebug', '0')
filter.req.subprocess_env['DEBUG'] = debug
" -->
<html>
<body>
<!--#if expr="${DEBUG} != 0" -->
DEBUG ENABLED
<!--#else -->
DEBUG DISABLED
<!--#endif -->
</body>
</html>
</pre></div>
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<span class="release-info">Release 3.3.1, documentation updated on January 29, 2007.</span>
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