Mod_Python and Web.py on Ubuntu

bseanvt — Wed, 09 Dec 2009 16:17:16 +0000

Download

First install mod_python for Apache and then restart/reload the server.

apt-get install libapache2-mod-python
/etc/init.d/apache2 force-reload
apache2ctl restart

Next grab the web.py framework from webpy.org. You can grab the tar or use easy_install depending on your setup.

wget http://webpy.org/static/web.py-0.33.tar.gz
tar xzvf web.py.tar.gz
cd web
sudo python setup.py install
# or if you use easy_install
easy_install web.py

Download this file http://www.aminus.net/browser/modpython_gateway.py?rev=106&format=raw This python package can (with this version) go anywhere in your python path “sys.path”. However, I placed it in the wsgiref directory. I’m running python2.6 so I did the following

# after downloading
mv modpython_gateway.py /usr/lib/python2.6/wsgiref/modpython_gateway.py

It’s important to remember that in the VirtualHost file you create the PythonHandler directive will need to reference this module. If you place it outside of the wsgiref directory remember to change the directive as well.

The VirtualHost

Now we need to create a VirtualHost for our application. You can run web.py apps without apache and this is good for development mode. To do this the command is

python pcode.py 4567

where the pcode.py is your web.py application filename and the 4567 is the port number you want to start the server on. I think it defaults to 8080. If you’re running apache or another web server port 80 will be in use. This is where mod_python (or cgi or fastcgi) come into play.

<VirtualHost *>
  ServerName py.seanbehan.com
  DocumentRoot /var/www/python/myapp

   #Aliases can trip you up! Pay attention here
   Alias /myapp /var/www/python/myapp
   <Directory /var/www/python/myapp>
      <IfModule python_module>
        PythonPath "sys.path +['/var/www/python/myapp']"
        AddHandler python-program .py
        # modpython_gateway is a file you'll need to download and place in wsgiref
        PythonHandler wsgiref.modpython_gateway::handler
        # This is your python program
        PythonOption wsgi.application pcode::main
        PythonOption SCRIPT_NAME /myapp
        PythonDebug on
      </IfModule>
    </Directory>
</VirtualHost>

Web.py Application

Web.py applications can be very simple. Everything can be placed in one file. In this example I created a file “pcode.py” and saved it to “/var/www/python/myapp/pcode.py”. The contents look like this

import web #this is the web.py frameword
web.webapi.internalerror = web.debugerror #lets capture errors for debugging

# map paths to classes
urls = (
    "/", "hello"
)

# this is the main from the PythonOption wsgi.application pcode::main from our VirtualHost
main = web.application(urls, globals()).wsgifunc()

class hello:
    def GET(self):
        #  web.header... otherwise you'll be prompted to save the file rather than view it in the browser
        web.header('Content-type','text/html')
        yield "Finally got web.py to work!"

if __name__ == "__main__":
    main.run()

Save the file, reload apache and visit the location on the web (In my case py.seanbehan.com/pcode.py/). Remember to include that last “/” after the pcode.py. You might get a “not found” message from web.py otherwise.

Pretty URLs

You can get pretty urls like “py.seanbehan.com/hello/world” if you use the mod_rewrite apache module.

a2enmod rewrite

You can either set up the rewrite rules in your VirtualHost or in a .htaccess file. I’ll do the .htaccess so I don’t have to reload the server for the changes to take effect.

In the same directory as your pcode.py file create a file “.htaccess” and in it place this code

<IfModule mod_rewrite.c>
  RewriteEngine on
  RewriteBase /
  RewriteCond %{REQUEST_URI} !^/icons
  RewriteCond %{REQUEST_URI} !^/favicon.ico$
  RewriteCond %{REQUEST_URI} !^(/.*)+code.py/
  RewriteRule ^(.*)$ pcode.py/$1 [PT]
</IfModule>

Troubleshooting

I ran into some trouble with the Alias in the VirtualHost file. It looks like this

Alias /myapp /var/www/python/myapp

This will map incoming urls to the full path on the filesystem so that your python program will run properly. I kept getting the not found error message from web.py without it. There might be a better way to set this up but this is how I got it to work.