My first Python project I walked into was in Twisted and was a MySQL abstraction layer and written by a crazy smart pair of folks where one of them was the king of early (unneeded) abtractions. On top of that, the tech lead wanted it to be ran in a Vagrant instance where he had set up most of the requirements, but not all. I had never even used a VM at the time, let alone worked on a project that dealt with multiple DB backends. I was handed it and told nobody had time to help, figure it out. Two weeks later, and I finally got the unit tests to pass and for it to actually start up.

The next one was likely the worst I've worked on. Twisted again. A shortened link redirector. Like, should be simple. I had to change one variable for my fist task in the codebase. I had to get help. It was hidden up three parent classes and three mixins away. Also turned out the majority of unit tests never would actually run because they didn't wait for the deferred events to actually return. Tests passed because they were not given the time to actually run assertions. Good times. :)