Django revisited

1 September 2007

Some time ago, I played around with Django. Having spent far too much time with writing my own blogging platform, I gave up.

In some ways, this was because I couldn’t get Django working on my current host. However, today, I spent a little time getting Django working at A2 Hosting, and this is how I did it.

(A big thanks to Jeff Croft and Seamusc—they laid out pretty much what needed to be done).

First of all I set up www2.petersmith.org (which is basically a sub-directory on my host). Let’s call the directory DJHOST/www2 Into DJHOST/www2 went .htaccess

AddHandler cgi-script .cgi
RewriteEngine on
RewriteRule \^(cgi-bin/.\_)---[L]
RewriteRule \^(media/.\_)---[L]
RewriteRule \^(admin_media/.\_)---[L]
RewriteCond %{<span class="caps">REQUEST_FILENAME</span>} !-f
RewriteRule \^(dj.cgi/.\_)---[L]
RewriteRule \^(.\_) /cgi-bin/dj.cgi/\1 [QSA,L]

I had enless problems, which I eventually traced back to the AddHandler line shown above.

Next, I created a cgi directory, i.e.

mkdir DJHOST/www2/cgi-bin

and in cgi-bin went dj.cgi

##!/usr/local/bin/python
#encoding: utf-8
"""
django.cgi
A simple cgi script which uses the django WSGI to serve requests.
Code copy/pasted from <span class="caps">PEP-0333</span> and then
tweaked to serve django.

http://www.python.org/dev/peps/pep-0333/\#the-server-gateway-side


This script assumes django is on your sys.path, and that your site code
is at
/home/mycode/mysite. Copy this script into your cgi-bin directory (or do
whatever you need to to make a cgi script executable on your system),
and then update the paths at the bottom of this file to suit your site.

This is probably the slowest way to serve django pages, as the python
interpreter, the django code-base and your site code has to be loaded
every time a request is served. FCGI and mod_python solve this problem, 
use them if you can.

In order to speed things up it may be worth experimenting with running
uncompressed zips on the sys.path for django and the site code, as
this can be (theorectically) faster. See PEP-0273 specifically Benchmarks.

http://www.python.org/dev/peps/pep-0273/).

Make sure all python files are compiled in your code base.  See

http://docs.python.org/lib/module-compileall.html)

import os, sys
#insert a sys.path.append("whatever") in here if django is not
#on your sys.path.
sys.path.append("/home/psmi045/public_html/www2/django")
sys.path.append("/home/psmi045/public_html/www2/psc")
sys.path.append("/home/psmi045/public_html/www2")
import django.core.handlers.wsgi
def run_with_cgi(application):
    environ = dict(os.environ.items())
    environ["wsgi.input'] = sys.stdin
    environ["wsgi.errors'] = sys.stderr
    environ["wsgi.version'] = (1,0)
    environ["wsgi.multithread'] = False
    environ["wsgi.multiprocess'] = True
    environ["wsgi.run_once'] = True
    if environ.get("HTTPS',"off') in ("on',"1'):
        environ["wsgi.url_scheme'] = "https'
    else:
        environ["wsgi.url_scheme'] = "http'
headers_set = []
headers_sent = []

def write(data):
    if not headers_set:
        raise AssertionError("write() before start_response()")
    elif not headers_sent:
#Before the first output, send the stored headers
    status, response_headers = headers_sent[:] = headers_set
    sys.stdout.write("Status: srn' status)
    for header in response_headers:
        sys.stdout.write("%s: srn' header)
        sys.stdout.write("rn')
        sys.stdout.write(data)
        sys.stdout.flush()

def start_response(status,response_headers,exc_info=None):
    if exc_info:
        try:
            if headers_sent:
            #Re-raise original exception if headers sent
            raise exc_info[0], exc_info[1], exc_info[2]
        finally:
            exc_info = None \#avoid dangling circular ref
    elif headers_set:
        raise AssertionError("Headers already set!")
        headers_set[:] = [status,response_headers]
        return write
    result = application(environ, start_response)
    try:
        for data in result:
            if data: \#don't send headers until body appears
                write(data)
            if not headers_sent:
                write(") \#send headers now if body was empty
    finally:
        if hasattr(result,"close'):
            result.close()
            #Change this to the directory above your site code.
            os.chdir("/home/psmi045/public_html/www2")
            #Change mysite to the name of your site package
            os.environ["<span class="caps">DJANGO_SETTINGS_MODULE</span>'] = "psc.settings"
            run_with_cgi(django.core.handlers.wsgi.WSGIHandler())

And that’s pretty much it. The rest was a matter of following Jeff’s instructions. Well amost it. Alas, A2 Hosting has several versions of Python lying around and not all of them have the necessary libraries; when I was using /usr/bin/python the MySQLdb module wouldn’t load. But that was fixed by moving to /usr/local/bin/python.