how to specify type of variables in python code example

Example 1: 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

Example 2: type declaration python

def greeting(name: str) -> str:
    return 'Hello ' + name