mod_python (Unix Power Tools, 3rd Edition)

42.9. mod_python

mod_python is an Apache module for running Python within the Apache webserver. It's much faster than CGI scripts and generally uses less resources overall. mod_python also allows advanced functionality such as maintaining persistent database connections across web requests and access to internal Apache APIs. Information on mod_python and distributions are available at http://www.modpython.org.

Apache's basic methodology for handling web requests is to deal with them in phases. There is a phase for each significant element of handling the request, including authentication, content generation, and logging. Apache modules can provide a seperate handler for each phase; mod_python simply allows you to write those handlers in Python. This allows complete control over everything Apache does to process a request.

A mod_python handler is a function that takes the Request object as an argument; a Request represents a single web request and contains all the information Apache knows about that request (requested URL, method, headers, and so forth).

Each phase's handler has a specific name that Apache recognizes (and uses in its configuration file): PythonHandler, PythonAuthenHandler, PythonLogHandler and so forth. Most mod_python scripts need to implement only the main handler, PythonHandler.

mod_python finds the appropriate function to call by dropping the leading Python from the handler name, and using an all-lowercase function name. Thus, most mod_python scripts will look something like this:

from mod_python import apache

def handler(request):
    request.content_type = "text/plain"
    request.send_http_header( )
    request.write("Hello World!")
    return apache.OK

This handler simply imports the apache API and then responds to every request with a plain text Hello World!. It returns apache.OK to tell Apache that the request was successful.

For more information on dealing with mod_python, read the documentation.

NOTE: One gotcha: mod_python's way of installing a mod_python handler is a little counterintuitive due to the way Apache handlers work. Make sure you understand how mod_python finds which module to import.

-- DJPH