A Python Mixin Class that Remembers Instances

remember.py

from __future__ import annotations

import gc
import sys
import weakref


class InstancesMixin:
    def __new__(cls, *args, **kwargs) -> Class:
        instance = super().__new__(cls)
        cls.instances.add(instance)
        return instance


class Foo(InstancesMixin):
    instances = weakref.WeakSet()


foo = Foo()
bar = Foo()
baz = Foo()
qux = Foo()

print(Foo.instances)

del foo

gc.collect()

print(Foo.instances)