Debugging WSGI applications can be pretty annoying. Because cgitb doesn't work with WSGI you need a wrapper for it.
There are many WSGI middlewares which allow the usage of cgitb with WSGI but they all have the same problem. When you have a syntax error in one of your files, the application dies with an utterly uninformative 500 INTERNAL SERVER ERROR.
When you start your application using the builtin server and an syntax error occurs, you get debug output in stderr. When there was no syntax error, Colubrid wraps the application in the builtin debug system and sends errors to the browser.