Django revisited

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/ww2 went .htaccess

AddHandler cgi-script .cgi
RewriteEngine on
RewriteRule ^(cgi-bin/.*)$ - [L]
RewriteRule ^(media/.*)$ - [L]
RewriteRule ^(admin_media/.*)$ - [L]
RewriteCond %{REQUEST_FILENAME} !-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 PEP-0333 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: %s\r\n' % status)
             for header in response_headers:
                 sys.stdout.write('%s: %s\r\n' % header)
             sys.stdout.write('\r\n')

        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['DJANGO_SETTINGS_MODULE'] = '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.