Infogami is a wiki application framework built on web.py.
Actual applications (like Open Library) are written by extending Infogami through two layers: plugins and templates.
Plugins are Python modules that get loaded into Infogami through a special API. They are invoked by submitting HTTP requests to the application, either HTML form posts or direct GET requests.
Plugins can use any library or application code that they wish, and they create Python objects to represent results, that then get expanded to HTML by templates.
Templates are a mixture of HTML text and user-written code, approximately in the spirit of PHP templates.
The user-written code is in a special-purpose scripting language that is approximately a Python subset, which runs in a hopefully-secure server-side interpreter (embedded in the Python app) that has limited access to system functions and resources.
from Infogami Developer Tutorial