By default the Google App Engine SDK doesn't run on Ubuntu 9.04 (Jaunty Jackelope)... You can fix it!
After a little searching I noticed neither posts about this issue nor a quick fix were top of the Google rankings... hoping to resolve that with this post and get all of us Ubuntu 9.04 (Jaunty) users up on App Engine. UPDATE: This post is now first when searching for "App Engine Ubuntu Jaunty Problem" and even "App Engine Ubuntu Jaunty" in one day, nice!
Once you download the SDK as usual and run one of your apps on a default Ubuntu 9.04 Jaunty install you will see errors galore, you see Ubuntu 9.04 ships Python 2.6 and App Engine is built on Python 2.5 and they are not friendly!
In a terminal install Python 2.5
They will coexist on the system.sudo apt-get install python2.5
Edit dev_appserver.py in your google_appengine directory
Change the first line in dev_appserver.py...#!/usr/bin/env python....to...
#!/usr/bin/env python2.5
App Engine should now load and run your apps properly!
I believe this is the simplest noninvasive way to let App Engine find what it wants, Python 2.5, and let Ubuntu carry on as it likes with Python 2.6 and beyond. Here is a source on this issue, commenters have many different solutions.
Hope this post helps at least one of you, -Ben