I like the implementation of the "Enum" class, especially the way they allow for enums with variant behavior and "abstract Enums" (something I could have used in Java recently).

But, ever since I found out about algebraic data types from other languages, I keep wanting those. There's not quite a good way to do those in Python. (I've used both "tuple subclass" and "__slots__," but both of those have their own little quirks.)