I was arch testing mod_wsgi for x86 stabilization and needed to test it so here is what I did.

First you will need to have apache working fine I have;

www-servers/apache-2.2.16

Then I installed ~x86 version of mod_wsgi;

emerge -av www-apache/mod_wsgi
[ebuild   R   ] www-apache/mod_wsgi-3.3

Next I created a little test;

def application(environ, start_response):
    status = '200 OK'
    output = 'Hello World!'
 
    response_headers = [('Content-type', 'text/plain'),
                        ('Content-Length', str(len(output)))]
    start_response(status, response_headers)
 
    return [output]

Saved it as /var/www/localhost/htdocs/hello.py

Next I edited vim /etc/apache2/vhosts.d/default_vhost.include
and added;

WSGIScriptAlias / /var/www/localhost/htdocs/hello.py

Next To enable mod_wsgi, you need to edit your /etc/conf.d/apache2 file and add '-D WSGI' to APACHE2_OPTS.

Here is my line;

APACHE2_OPTS="-D DEFAULT_VHOST -D INFO -D MANUAL -D SSL -D \ 
SSL_DEFAULT_VHOST -D LANGUAGE -D PHP5 -D WSGI"

Now when you restart the server you should see on http://localhost/ the "Hello World!" message.

Thats it!