I'd like to type hint a function like this:
from types import Iterable
def func(thing: Iterable[str]) -> None:
for i in range(10):
for x in thing:
do_thing(x)
PyCharm will (correctly) let me get away with passing in a generator to this function, but I want to type hint it in a way that it won't allow me to, while still accepting other iterables.
Using Sequence[str] isn't an option, iterables like KeyView aren't sequences, but I would still like to be able to include them.
Someone mentioned using a Union with a Sequence + KeyView, which would work, but I was wondering if there was a more elegant and universal solution
Of course, I could just convert thing to a list no matter what, but I'd rather just have this function type hinted correctly.
Using Python 3.7
Unfortunately I think this is just not possible with Python's type system.
Straight from Guido (source):
Our type system doesn't allow you to express that -- it's like asking for any Animal except Cat. Adding an "except" clause like that to the type system would be a very difficult operation.
Since there's no solution, I'm going to close this as "won't fix".
His suggestion:
Yeah, the practical solution is Sequence|Set|Mapping. The needed negation is years off.