singleton.py

from weakref import WeakValueDictionary

class Singleton(type):
    _instances = WeakValueDictionary()

    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            instance = super(Singleton, cls).__call__(*args, **kwargs)
            cls._instances[cls] = instance
        return cls._instances[cls]


class Config(metaclass=Singleton):
    pass

It's a bit complicated snippet. I would use python module as a singleton.

@easysugar Agreed, python modules are pure singletons and they don't have much complexity but I think I like the explicit usage of this construction more(even if I'll use modules anyway:)):

cfg = Config()

or even using context managers:

with Config() as cfg:
    pass

instead of

from config as cfg