How to investigate web script not running?

[Gilles]

Hello

I'm trying to run my very first FastCGI script on an Apache shared
host that relies on mod_fcgid:
==============
#!/usr/bin/python
from fcgi import WSGIServer
import cgitb

# enable debugging
cgitb.enable()

def myapp(environ, start_response):
        start_response('200 OK', [('Content-Type', 'text/plain')])
        return ['Hello World!\n']

WSGIServer(myapp).run()
==============

After following a tutorial, Apache complains with the following when I
call my script:
==============
Internal Server Error

The server encountered an internal error or misconfiguration and was
unable to complete your request.
==============

Generally speaking, what tools are available to investigate issues
when running a Python web app?

Thank you.