Wednesday, January 21, 2009

How-to: Setting up Google App Engine for Simple Sites

I wanted to find a simple way to publish a custom website or two for low cost, and settled on Google App Engine as the best current solution. This post focuses on getting an Eclipse environment up and running to debug and publish your Python and other code to Google App Engine.

I initially planned to do the site in Flex, but changed my mind after looking at SEO problems with Flash applications. It does look like there are solutions for getting search engines to index Flash content, but I haven't put in the effort to really explore them yet. My sites are (for the moment) done in plain old HTML with CSS. The only twist is that the Python code strings together several fragments of HTML code to build each page. (I'll talk about that in a later post.)


The Basics
I won't repeat what Nick Berardi already said in his great how-to post. Please check that out for step-by-step instructions on getting your own domain, creating an app engine application, and uploading your content with one command. (You can do this without a domain, but since it's a whopping $10/year there is little reason not to).

Once you have followed these instructions & have an engine application connected to your domain, there are still a couple of steps you need to follow so you can debug the Python portion of the code.

The following is adapted from Google's tutorial here:
  1. Install Python 2.6 if you have not already done so. (There is a newer version, but this is what I used.)

  2. Install pydev eclipse extension for Eclipse through the Eclipse update manager (Help | Software Updates in Eclipse) using this url: http://pydev.sourceforge.net/updates/

  3. Tell PyDev where to find the interpreter (create a pydev project and Eclipse will prompt you to do this). I just browsed to the default install location of "Program Files/Python26/python.exe".

  4. Install the google app engine SDK if you have not already done so.

  5. Create the "helloworld.py" and "app.yaml" files as described in Google's Tutorial.

  6. Test the dev server. I kicked off my mini program with this command-line:
    • "\Program Files\Google\google_appengine\dev_appserver.py"
      "/Users/Erik/projects/PythonTestBed/src"
    • This runs the dev app server and kicks off the app.yaml script in
      my PythonTestBed/src directory.

  7. Fire up a browser with http://localhost:8080. It should show "hello world".

Debugging GAE Python in Eclipse
You can run Python programs in two ways (I tried both & they worked):
  • By selecting "Python run" in Eclipse.
  • By going to the http://localhost:8080 page as above & refreshing it.

I like to view the Python output inside of Eclipse, so I needed to tell PyDev where the api libraries are under Window | Preferences:



The bottom five folders were added with the "New Folder" button. I probably don't need anything other than the appengine, webob and yaml folders for what I'm doing, but I added the others anyway.

I ran into a hitch in calling urlfetch (I needed to parse an RSS stream and feed it into my site as well-behaved HTML. I'll talk about this in a separate post). Because Google uses a proxy to do the actual fetch, it wouldn't run from my local machine until I imported some stubs:

…and then set the stubs up before calling urlfetch in my code…

This will get you up and running. Getting the Python, html, css and javascript pieces uploading and working together will be the subject of a future post.
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