how to declare parameter types python code example

Example 1: python function argument type

def pick(l: list, index: int) -> int:
    return l[index]

Example 2: typing generator python

# Iterator
def infinite_stream(start: int) -> Iterator[int]:
    while True:
        yield start
        start += 1

# Generator        
def infinite_stream(start: int) -> Generator[int, None, None]:
    while True:
        yield start
        start += 1