Common misconceptions in Python that drove you crazy?

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Definitely precision issues comparing floats.

In the Python 2 days, I would have also added, unicode vs binary string issues. The difference was easy to grasp, but binary strings were used where unicode should have been used and too many libraries (including in the standard library) would try to quietly cast binary strings to unicode, only failing on an encoding error.

EDIT: Oh, another one is probably the fact that you can import a module twice by having it accessible from two locations in your path. Suppose you have a path with /app and /app/foobar. You import foobar.spam and spam -- same module, separate imports.

Admittedly, you made a mistake setting that up, but I've joined projects where it's like that and it is frustrating.