I always point people here for a decent write-up of some "gotchas": https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments https://docs.python

I always point people here for a decent write-up of some "gotchas": https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments https://docs.python-guide.org/writing/gotchas/#mutable-defau... . What is your list of "these little hang ups you only know about once you’ve pulled your hair out" if you don't mind sharing?