Here are a couple of functions:

def avg(vals: Sequence[float]):
    return sum(val for val in vals) / len(vals)

def foo():
    the_dict = {'a': 1., 'b': 2.}
    return avg(the_dict.values())

PyCharm 2022.3 warns about the_dict.values() in the last line:

Expected type 'Sequence[float]', got _dict_values[float, str] instead

But .. those values can be iterated across and have their length taken.

I tried

def avg(vals: Union[Sequence[float], _dict_values]):

which seems insane, but also didn't work.

Suggestions?

I can turn off the typing for that arg, but I am curious what the right thing is.

CodePudding user response：

_dict_values is not a Sequence (it's closer to an Iterator). Lucky avg doesn't require everything Sequence ensures. You only need Iterable[float] for sum and Sized for len().

from typing import Iterable, Protocol, Sized


class SupportsFloatMean(Iterable[float], Sized, Protocol):
    ...


def avg(vals: SupportsFloatMean):
    return sum(val for val in vals) / len(vals)

CodePudding user response：

Reference: https://docs.python.org/3/library/stdtypes.html?highlight=dict#dictionary-view-objects

The objects returned by dict.keys(), dict.values() and dict.items() are view objects. Dictionary views can be iterated over to yield their respective data, and support membership tests.

iter(dictview): Return an iterator over the keys, values or items (represented as tuples of (key, value)) in the dictionary.

from typing import Union, Iterable, Sized


def avg(vals: Union[Iterable[float], Sized]) -> float:
    return sum(val for val in vals) / len(vals)


def foo() -> float:
    the_dict = {'a': 1., 'b': 2.}
    return avg(the_dict.values())


if __name__ == '__main__':
    print(foo())