In Python you don't know what you receive and someone could have modified something in an object somewhere in the code that will break down the line in unexpected ways.

Python does not have any type checking those are just annotation it does not enforce anything.

https://docs.python.org/3/library/typing.html

"Note The Python runtime does not enforce function and variable type annotations. They can be used by third party tools such as type checkers, IDEs, linters, etc."