Python on the Web

If you've ever seen Python in action, even at a distance, I'm sure you'll agree that it looks pretty neat. And the combination of development speed, out-of-the-box power, and stunning syntax usually means you end up with one thing... elegant, maintainable solutions, quickly. And lets face it, that's just what web developers are looking for right?

I'll let you judge for yourself...

In this article we're going to be using Python to write some small and (hopefully) interesting examples, starting with simple form handling and ending with a complete, full featured (upload limit, file types etc.) upload script that you can use in your websites!

If you haven't guessed it already this is a Python article, so if you're new to the language I highly recommend reading Martin Tsachev's Getting Started with Python before reading this one. if you need a quick intro to Python CGI, skim over Preston Landers' "Writing CGI Programs in Python".

Before we get going, you'll need a few things before you can run the examples in this article:

1. A web server set up to handle CGI (tested with Apache)
2. The latest version of Python from www.python.org

Creating a Form to Display User Details

Possibly the most important thing a web application does is collect user input. And like most things, Python has just the module we need in its Standard Library.

Let's jump right in and write a small function to display the user's details if any where entered. (For this we'll assume our form looks like this... three input boxes called - 'name', 'age' and 'email'. A check box called 'done' and a 'submit' button)

#!/usr/bin/env python

import cgi

form = cgi.FieldStorage()

def values(fields):
 for value in fields:
  if value in form: print form[value].value + '<br />'

if __name__ == '__main__':
 
 print 'Content-Type: text/htmln'

 if 'submit' and 'done' in form:
  values(('name', 'age', 'email'))
 else:
  print 'if you were directed here in error please visit here.com'

This is very simple but it gives you an idea of how easy working with forms is when you strip away all the crap!

In this example (and most of the examples in this article) we start by importing the 'cgi' module and creating an instance of the FieldStorage() class to store our form values. Next we define a new user function called values() which takes a sequence of field names and iterates over them, printing the value if the one was set. Finally before the function outputs anything we check if the 'submit' and 'done' fields exist.

Ok, chances are you noticed this but just for clarity: forms in Python work like any dictionary, with the exception that you have to follow the call by the variable you want access from that key i.e. form['key'].value gives you the value.