More function signatures

Here are a few more examples of adding type hints to function signatures.

If a function does not explicitly return a value, give it a returntype of None. Using a None result in a statically typedcontext results in a type check error:

def p() -> None:
    print('hello')
 
a = p()  # Error: "p" does not return a value

Make sure to remember to include None: if you don’t, the functionwill be dynamically typed. For example:

def f():
    1 + 'x'  # No static type error (dynamically typed)
 
def g() -> None:
    1 + 'x'  # Type check error (statically typed)

Arguments with default values can be annotated like so:

def greeting(name: str, excited: bool = False) -> str:
    message = 'Hello, {}'.format(name)
    if excited:
        message += '!!!'
    return message

args and *kwargs arguments can be annotated like so:

def stars(*args: int, **kwargs: float) -> None:
    # 'args' has type 'Tuple[int, ...]' (a tuple of ints)
    # 'kwargs' has type 'Dict[str, float]' (a dict of strs to floats)
    for arg in args:
        print(arg)
    for key, value in kwargs:
        print(key, value)