This is my first attempt to make a Python decorator, and I humbly admit to drawing inspiration from a number of StackOverflow posts while doing so. When I scavenged the __instancecheck__ method, the last two asserts stopped triggering, but now PyCharm's built-in linter isn't happy with the very last assert.
Expected type 'Union[type, Tuple[Union[type, Tuple[Any, ...]], ...]]', got 'Multiton' instead.
What is the root of the typing problem, and how can it be fixed?
Addition, after making the __init__ change recommended by a commenter another warning surfaces.
Local variable 'instance' might be referenced before assignment.
class Multiton(object):
""" When init parameters match, reuse an old initialized object instead of making a new one. """
def __init__(self, cls):
# self.__dict__.update({'instances': list(), 'cls': 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)
The false warnings are PyCharm bugs which hopefully the fine folks at JetBrains will remedy soon.
https://youtrack.jetbrains.com/issue/PY-38590 https://youtrack.jetbrains.com/issue/PY-49966