In Python documentation for typing & type hints we have the below example: Vector = List[float] def scale(scalar: float, vector: Vector) -> Vector: return [scalar * num for num in vector] Vector type alias clearly shows that type aliases are useful for simplifying complex type signatures. However, what about aliasing primitive data types? Let's contrast two basic examples of function signatures: URL = str def process_url(url: URL) -> URL: pass vs. def process_url(url: str) -> str: pass Version with type alias URL for primitive type str is: self-documenting (among others, now I can skip documenting returned value, as it should be clearly an url), resistant to type implementation change (I can switch URL to be Dict or namedtuple later on without changing functions signatures). The problem is I cannot find anyone else following such practice. I am simply afraid that I am unintentionally abusing type hints to implement my own ideas instead of following their intended purpose. Note from 2020-10 Python 3.9 introduces "flexible function and variable annotations", which allows to make annotations like: def speed_1(distance: "feet", time: "seconds") -> "miles per hour": pass def speed_2( distance: Annotated[float, "feet"], time: Annotated[float, "seconds"] ) -> Annotated[float, "miles per hour"]: pass Which renders aliasing data types for documenting purposes rather redundant! See: https://www.python.org/dev/peps/pep-0593/ https://realpython.com/python39-new-features/#annotated-type-hints Continue reading...
