Fri, 13 Nov 2009

This Python on the Toilet issue is also available as PDF.

WSGI is a Python standard for how web servers can interact with web frameworks. It’s one of my favorite standards: it’s simple yet very powerful.

To write a WSGI web application you only need to create one function.

def my_app(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return repr(environ)

The function receives a environ argument – a dictionary with all the environment variables. The start_response function can be called with the status line and a list of headers as soon as you’re ready to send output.

New Python releases contain the library wsgiref which can be used to get started quickly with a simple web server (that should not be used in production).

pre..from wsgiref.simple_server import make_server
httpd = make_server(‘’, 8000, my_app)

Save these two snippets in a file e.g. myapp.py and execute it with Python. This will serve the sample application on port 8000. Try it out.

You don’t usually want to write your own application directly on top of WSGI. But most frameworks now implement WSGI which has led to better interoperability. If you still want to use WSGI directly, there are a ton of good tools such as WebOb?, “Werkzeug” or “Paste”. I used WebOb to easily build a REST service framework called WsgiService.

For more information I recommend the specification for WSGI which is a good read.

This post is part of the Python on the toilet series.