Correct type hint for multiple return values-CodePudding

Let's say that I have a function returning a single value in some cases and multiple values (i.e. tuple) in other cases.

def foo(a: int, b: int, flag: bool):
    if flag:
        return a
    else:
        return a, b

What is the correct type annotation for the return value of this fuction?

I can propose something like this:

def foo(a: int, b: int, flag: bool) -> Tuple[int, Optional[int]]:
    if flag:
        return a
    else:
        return a, b

But the main thing that I don't like in this code is that in case when the function returns a single value, that value is not a tuple. So to make this work properly I should remake the function to

def foo(a: int, b: int, flag: bool) -> Tuple[int, Optional[int]]:
    if flag:
        return (a,) 
    else:
        return a, b

Which is something that I don't want to do. Any thoughts?

CodePudding user response：

You want to use typing.Union to indicate that the function can return either one type of thing or another. For example, if you had a function that could either return an int or a str, then it's return type would be Union[int, str].

So,

def foo(a: int, b: int, flag: bool) -> Union[int, Tuple[int, int]]:

If you're using Python 3.10, there's a better way to write a union: int | Tuple[int, int]