Setting up debugging for Google AppEngine projects in Eclipse

When I made the move from Windows to OSX and Python development one of the things I wanted to experiment with has been Google’s AppEngine. I installed the SDK and setup the plugin for Eclipse but ran into a few issues I wanted to make note of since I think other could probably benefit from it as well. I’ll mention I’m on OSX 10.6.8 using Eclipse for Java Version Helios SR 2.

Creating a new AppEngine project in Eclipse

With the plugin installed you get an AppEngine project template listed under PyDev.
Screen shot 2011-08-30 at 8.48.55 PM
Clicking Next displays the standard Eclipse dialog for a new project where you enter the name and optionally a few other project settings. However, it’s the dialog after that where I had my first question where you’re prompted for the Google App Engine Directory which in my case corresponds to:

/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/

Google instructions for development in Eclipse didn’t answer this question and it wasn’t immediately obvious to me. At any rate, once this path is set correctly you’ll immediately see a list of AppEngine modules to be included on the PYTHONPATH:
Screen shot 2011-08-30 at 9.14.38 PM

Configuring the Project’s Python Interpreter

After I successfully created the AppEngine project I wanted to look at the appengine-boilerplate for HTML5 which is based on HTML5 boilerplate which is well worth checking out. Next, I used the Google AppEngine Console to create a new application called “helloworld954” then copied the boilerplate files into my project and edited the app.yaml file to set the application name:

application: helloworld954

I then ran the project and everything looked ok but when I hit the page from the browser (http://localhost:8080) I got:

ImportError: No module named cgi

Which I subsequently discovered more information about here.
Now, IIRC my MacBook Pro came with Python 2.6 as the default version though v2.5 was installed as well and given AppEngine is, as of this writing, based on v2.5 I figured rather than tweaking dev_appserver.py as mentioned on that prior link I figured I’d first try the proper Python version. I right clicked my project from the package explorer and selected Properties then clicked the PyDev – Interpreter/Grammar option then clicked the “Click here to configure an interpreter not listed” link (blue link below).
Screen shot 2011-08-30 at 9.36.44 PM
Next, on the preferences dialog (which I won’t screenshot here as it’s too big) I clicked New… and added a new interpreter option for “Python v2.5” with a path of:

/Library/Frameworks/Python.framework/Versions/2.5/Resources/Python.app/Contents/MacOS/Python

Btw, I think I tried the symlink but that wasn’t allowed (again, I think).
At any rate, once I saved those changes voila the boilerplate project started working. Ah, one step I overlooked was setting up a debug configuration for this project:
Screen shot 2011-08-30 at 9.49.13 PM
The main module for the application has to be Google’s dev_apperser.py file which is located here on my machine:

/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/dev_appserver.py

Also, under the (x)= Agruments tab I set the Program Arguments to “.” for the current working directory and for “Working Directory” I selected “Other” with a value of “$(workspace_loc:starterkit}” Note, starterkit is the name of my project.
The final result:
Screen shot 2011-08-30 at 9.53.42 PM
Hopefully, this helps someone else, it will certainly help me months from now when I trying to do the same thing again so I won’t have try and recall all these steps.