I tried to write a little Hello World app for the app engine this evening and ran up against a sneaky problem. I used some quick tutorial code and came up with an app that looked like this:

And it ran ok as a standalone program, but under dev_appserver.py it would hang, with no errors, and consume all of my memory and CPU time. Sucks.

After messing around a bit, I found that my problem was calling app.run() instead of app.cgirun().