"Hello world" in Python CGI Web Programming in 5 minutes

I have lotta Python programs for bioinformatics research. I wanted to put them onto the web. I only developed Web apps in PHP before. And it seemed to be a big pain for porting a Python program to the web. But, I figured out in 5 minutes.
First, you need an Apache server on your Linux/Mac OS/Windows box. If you are gonna use data base, you need a database server. There are tons of blogs addressing these issues. So I won't be gossipy here. Suppose everything we mention below happens on your server-even web browsing.
Second, configure cgi in Apache. There are many ways to run a Python program on a web/http interface. I think CGI is the easiest. Assume you are on your own server and using all default settings. On Ubuntu Linux 9.04, the default configuration file for your default website is /etc/apache2/sites-available/default Open it, find the part for cgi directory, and make it like this

ScriptAlias /cgi-bin/ /var/www/cgi-bin/
        
                AllowOverride None
                Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
                Order allow,deny
                Allow from all
                AddHandler cgi-script .py                       # tell Apache to handle every file with .py suffix as a cgi program
                AddHandler default-handler .html .htm  # tell Apache to handle HTML files in regular way
        

The line

ScriptAlias /cgi-bin/ /var/www/cgi-bin/

specifies the path of cgi codes and the actual directory of your program. So when you type http://127.0.0.1/cgi-bin, the Apache will look into the directory /var/www/cgi-bin/ of your localhost.
Now restart your apache. On Ubuntu Linux, by default installation and configuration, it is

sudo /etc/init.d/apache2 restart

Third, write up a Hello, World! program. Save it as hello.py and give it execution privilege for anyone.

#!/usr/bin/env python
print "Content-Type: text/html"
print
print """\






Hello World!
"""

Now open http://127.0.0.1/cgi-bin/hello.py in your web browser and you shall see a hello world in it.
If you have any error, e.g., 500 error, please check your Apache log file. It shall tell you something. You can find errors like what you have seen from a standard Python interpreter.
Reference: http://webpython.codepoint.net/cgi_tutorial