mod_wsgi/python sys.path.exend problems

Question

I'm working on a mod_wsgi script.. at the beginning is:

sys.path.extend(map(os.path.abspath, ['/media/server/www/webroot/']))

But I've noticed, that every time I update the script the sys.path var keeps growing with duplicates of this extension:

['/usr/lib64/python25.zip'
'/usr/lib64/python2.5'
'/usr/lib64/python2.5/plat-linux2'
'/usr/lib64/python2.5/lib-tk'
'/usr/lib64/python2.5/lib-dynload'
'/usr/lib64/python2.5/site-packages'
'/usr/lib64/python2.5/site-packages/Numeric'
'/usr/lib64/python2.5/site-packages/gtk-2.0'
'/usr/lib64/python2.5/site-packages/scim-0.1'
'/usr/lib/python2.5/site-packages'
'/media/server/www/webroot'
'/media/server/www/webroot'
'/media/server/www/webroot'
'/media/server/www/webroot']

It resets every time I restart apache.. is there any way to make sure this doesn't happen? I want the module path to be loaded only once..

Answer 1

One fairly simple way to do this is to check to see if the path has already been extended before extending it::

path_extension = map(os.path.abspath,['/media/server/www/webroot/']) 
if path_extension[0] not in sys.path:
    sys.path.extend(path_extension)

This has the disadvantage, however, of always scanning through most of sys.path when checking to see if it's been extended. A faster, though more complex, version is below::

path_extension = map(os.path.abspath,['/media/server/www/webroot/']) 
if path_extension[-1] not in reversed(sys.path):
    sys.path.extend(path_extension)

A better solution, however, is probably to either add the path extensions to your PYTHONPATH environment variable or put a .pth file into your site-packages directory:

http://docs.python.org/install/index.html

Answer 2

No need to worry about checking or using abspath yourself. Use the ‘site’ module's built-in addsitedir function. It will take care of these issues and others (eg. pth files) automatically:

import site
site.addsitedir('/media/server/www/webroot/')

(This function is only documented in Python 2.6, but it has pretty much always existed.)

Answer 3

The mod_wsgi documentation on code reloading covers this.