Static typing in python3: list vs List [duplicate]

Question

What is the difference between using list and List when defining for example the argument of a function in python3? For example, what is the difference between

def do_something(vars: list):

and

def do_something(vars: List):

The documentation says:

class typing.List(list, MutableSequence[T])

Generic version of list. Useful for annotating return types.

but I'm not entirely sure what the above means.

I have similar questions for: dict vs Dict, set vs Set, etc.

Answer 1

Not all lists are the same from a typing perspective. The program

def f(some_list: list):
    return [i+2 for i in some_list]

f(['a', 'b', 'c'])

won't fail a static type checker, even though it won't run. By contrast, you can specify the contents of the list using the abstract types from typing

def f(some_list: List[int]) -> List[int]:
    return [i+2 for i in some_list]

f(['a', 'b', 'c'])

will fail, as it should.