Giving names to returned values with python type hints

Question

Let's say I have a function like

def basic_stats(data: List[float]):
    """This returns a tuple with the mean and median values of the data
    """
    return (np.mean(data), np.median(data))

and I want to use type hints to self-document the code instead of a comment. The standard way isn't super clear:

def basic_stats(data: List[float]) -> Tuple[float, float]:

because you can't tell by looking at the hint which output float is which.

Sometimes I've seen people do this:

def basic_stats(data: List[float]) -> Tuple["mean", "median"]:

which compiles just fine, and actually gives the humans what they need, but doesn't help the IDEs or mypys. (Although I'm yet to see those actually be useful in the real world yet, but that's maybe a different story.)

Is there any way to do both which is valid, pythonic, and useful? I'd like to be able to do something like this:

def basic_stats(data: List[float]) -> Tuple[mean:float, median:float]:

or should we just stick with something like

def basic_stats(data: List[float]) -> Tuple["mean:float", "median:float"]:

Or anything coming in a proposed PEP to solve this?

brunson · Answer

There's nothing that can do that in the type hints. I can think of several reasons not to, such as overwriting a variable in the caller with the same name you're returning.

An approach might be to return a named tuple using namedtuple from collections (https://docs.python.org/3/library/collections.html#collections.namedtuple) or a NamedTuple from the typing module (https://docs.python.org/3/library/typing.html#typing.NamedTuple)

Giving names to returned values with python type hints

1 Answers