Two doubtful warnings.

The following code runs, but PyCharm issues two warnings. 

I used the debugger to confirm that __init__ happens before __call__, yet the following warning is issued:
warning: Local variable 'instance' might be referenced before assignment

I used isinstance to verify that the object types are as intended yet there is a warning on the second check:
Expected type 'Union[type, Tuple[Union[type, Tuple[Any, ...]], ...]]', got 'Multiton' instead

Thoughts?

class Multiton:
    """ When init parameters match, reuse an old initialized object instead of making a new one. """
    def __init__(self, cls):
        self.instances = list()
        self.cls = cls

    def __call__(self, *args, **kwargs):
        # make a key with the parameters
        key = (args, kwargs)

        # search for a matching old instance
        found = False
        for instance in self.instances:
            if instance['key'] == key:
                found = True
                break

        # if not found then create a new instance
        if not found:

            instance = {'key': key, 'object': self.cls(*args, **kwargs)}
            self.instances.append(instance)

        return instance['object']

    def __instancecheck__(self, other):
        return isinstance(other, self.cls)


@Multiton
class YourClass:

    def __init__(self, number):
        self.number = number


yc_1 = YourClass(1)
yc_2 = YourClass(2)
yc_two = YourClass(2)

assert yc_1 != yc_2
assert yc_2 == yc_two

assert not isinstance(yc_1, Multiton)
assert isinstance(yc_1, YourClass)