Singleton pattern

singleton.py

class Singleton(type):
    _instances = {}

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


class MyClass(metaclass=Singleton):
    def __init__(self):
      self.a = 234
      

aa = MyClass()
aa.val  # 234
bb = MyClass()
bb.val = 654
aa.val  # 654

id(aa) == id(bb)