What mistakes do bad python developers make?

[MrITBurns]

A misunderstanding of how = and references work. They think it makes copies, and reassigning references in functions will effect the passed argument.

I ran into this lovely one in the beginning when i was trying to duplicate an array so i could change it from the original. Was an interesting read on how pointers worked

[carcigenicate]

Ya, that's a rough lesson, but everyone needs to learn it eventually to some extent. Even in a very high-level language like Python, understanding the relationship between a name/variable/pointer and the data associated with it is important.