The problem with Python (and dynamically typed languages in general) is not so much knowing the language, but understanding the code that people write with it.
Since there are no type annotations to help your understanding of the code, you need to keep a lot in your head, as opposed to statically typed languages.
That’s not been my experience at all, but I could see it being confusing at first.
Also, we do have type annotations now. They’re not universally used, and definitely not required, but mypy and friends can go a long way toward finding type issues even without them.
Since there are no type annotations to help your understanding of the code, you need to keep a lot in your head, as opposed to statically typed languages.