Guide: Deploying web.py on IIS7 using PyISAPIe

I spent the last week travailing away, trying to painfully find a way to deploy a web.py based API on IIS7 using PyISAPIe. As frustrations had begun to mount up, I had nearly decided to give up. Being a die-hard Linux and Mac guy, I despise having to work on Windows. Here I was, not only forced to work on Windows, but to find a solution for a problem that left no leaves unturned in its effort to drive me crazy. As if someone decided all this misery wasn’t quite enough, I had to work with a remote desktop session in order to research, tweak, bang my head, and get things to work. Eventually, I cut through massive frustration and despair, managing to find a satisfactory solution. I almost danced in excitment and relief, letting out all sorts of expletives directed at Windows in general and IIS in particular.

To get back to the important question of deploying a web.py script on IIS7 using PyISAPIe, I will make it such that this guide will list down various steps I took, including snippets of relevant code I changed, to tame the beast. I can only hope that what is below will help a poor, miserable soul looking for help as I did (and found none).

I worked with PyISAPIe because I had successfully deployed multiple Django websites on IIS7 on it. The script in question was going to be a part of another Django website (though acting independently). It only made sense to use PyISAPIe for it as well.

First and foremost, I had to install the web.py module on the system. Having had trouble before with IIS with web.py installed through easy_install, I decided to be safe and installed it from source.. Getting web.py to work with PyISAPIe required a small hack (I notice I may make it sound as though it all came down to me in a dream, but in reality, it took me days to figure it out, and clearly after much anguish and pain). In the file Lib\site-packages\web\wsgi.py lies the following function:

def _is_dev_mode():
    # quick hack to check if the program is running in dev mode.
    if os.environ.has_key('SERVER_SOFTWARE') \
        or os.environ.has_key('PHP_FCGI_CHILDREN') \
        or 'fcgi' in sys.argv or 'fastcgi' in sys.argv \
        or 'mod_wsgi' in sys.argv:
            return False
    return True

In its pristine state, when web.py is imported from a source file through PyISAPIe, an exception is thrown. The exception, while I don’t have the exact message, is about it complaining about sys.argv not having an attribute argv, which reads fishy. Since the function _is_dev_mode() only checks whether web.py is being run in development mode, I thought I didn’t care about it since I wanted everything to run in production mode. I edited the function such that its body would be bypassed, while it returned a False boolean value. It looked like this (the important changes I made are highlighted):

def _is_dev_mode():
    return False
    # quick hack to check if the program is running in dev mode.
    if os.environ.has_key('SERVER_SOFTWARE') \
        or os.environ.has_key('PHP_FCGI_CHILDREN') \
        or 'fcgi' in sys.argv or 'fastcgi' in sys.argv \
        or 'mod_wsgi' in sys.argv:
            return False
    return True

This innocuous little addition did away with the exception.

Next up, I used default Hello World-esque example of web.py found on their site to test the deployment (of course, I went on to use my original API script, which was far too complex to trim down and fit into as an example). I called it code.py (I placed it inside the folder C:\websites\myproject). It looked like this:

  import web
  urls = (
      '/.*', 'hello',
      )
  class hello:
      def GET(self):
          return "Hello, world."
  application = web.application(urls, globals()).wsgifunc()

It was pretty simple. You have to pay particular attention on the call to web.application. I called the wsgifunc() to return a WSGI-compatible function to boot the application. I prefer WSGI.

I set up a website under IIS using the IIS Management Console. Since I was working on a 64-bit server edition of Windows and had chosen to use 32-bit version of Python and all modules, I made sure to enable 32-bit support for the application pool being used for the website. This was important.

I decided to keep the PyISAPIe folder inside the folder where code.py rested. This PyISAPIe folder contained, of import, the PyISAPIe.dll file, and the Http folder. Inside the Http folder, I placed the most important file of all: the Isapi.py. That file could be thought of as the starting point for each request that is made, what glues the Request to the proper Handler and code. I worked with the Examples\WSGI\Isapi.py available as part of PyISAPIe. I tweaked the file to look like this:

from Http.WSGI import RunWSGI
from Http import Env
#from md5 import md5
from hashlib import md5
import imp
import os
import sys
sys.path.append(r"C:\websites\myproject")
from code import application
ScriptHandlers = {
	"/api/": application,
}
def RunScript(Path):
  global ScriptHandlers
  try:
    # attempt to call an already-loaded request function.
    return ScriptHandlers[Path]()
  except KeyError:
    # uses the script path's md5 hash to ensure a unique
    # name - not the best way to do it, but it keeps
    # undesired characters out of the name that will
    # mess up the loading.
    Name = '__'+md5(Path).hexdigest().upper()
    ScriptHandlers[Path] = \
      imp.load_source(Name, Env.SCRIPT_TRANSLATED).Request
    return ScriptHandlers[Path]()
# URL prefixes to map to the roots of each application.
Apps = {
  "/api/" : lambda P: RunWSGI(application),
}
# The main request handler.
def Request():
  # Might be better to do some caching here?
  Name = Env.SCRIPT_NAME
  # Apps might be better off as a tuple-of-tuples,
  # but for the sake of representation I leave it
  # as a dict.
  for App, Handler in Apps.items():
    if Name.startswith(App):
      return Handler(Name)
  # Cause 500 error: there should be a 404 handler, eh?
  raise Exception, "Handler not found."

The important bits to note in the above code are the following:

• I import application from my code module. I set the PATH to include the directory in which the file code.py is so that the import statement does not complain. (I’ve to admit that the idea of import application and feeding it into RunWSGI came to while I was in the loo.)
• I defined a script handler which matches the URL prefix I want to associate with my web.py script. (In hindsight, this isn’t necessary, as the RunScript() is not being used in this example).
• In the Apps dictionary, I again route the URL prefix to the lambda function which actually calls the `RunWSGI` function and feeds it application.
• I also imported the md5 function from the hashlib module instead of the md5 module as originally defined in the file. This was because Python complained about md5 module being deprecated and suggested instead of use hashlib.

And that’s pretty much it. It worked. I couldn’t believe what I saw on the browser in front of me. I danced around my room (while hurling all kinds of expletives).

There’s a caveat though. If you have specific URLs in your web.py script, as I did in my API script, you will have to modify each of those URLs are add the /api/ prefix to them (or whatever URL prefix you set in the Isapi.py. Without that, web.py will not match any URLs in the file.

What a nightmare! I hope this guide serves to help others.

Thank you for reading. Good bye!

PS: If you want to avoid using PyISAPIe, there is a simpler way of deploying web.py on IIS. It is documented crudely over here.