The docs are full of remarks like "removed in 3.0 and reintroduced in 3.4" or "deprecated in 3.10", etc. A big one is the removal of the loop parameter in asyncio, but a lot of asyncio internals are (still?) undergoing significant changes, as getting the shutdown behavior correct is surprisingly difficult. Personally it's never cause me any issues - I'm always on board with the changes.

Asyncio was explicitly marked as provisional for years and most of the incompatible changes happened during that time. Same goes for typing. The rest of the language is very very stable.

One of the few that I remember is fractions.gcd() -> math.gcd().

See https://docs.python.org/3.0/library/fractions.html#fractions... , https://docs.python.org/3.5/library/fractions.html#fractions... , https://docs.python.org/3.9/library/fractions.html (gone), https://docs.python.org/3.5/library/math.html#math.gcd