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class Foo: def __init__(self): self.__secret = 42 def get_secret(self): return self.__secret f = Foo() print(f._Foo__secret) # 42 – still accessible, but harder to accidentally access python 3 deep dive part 4 oop high quality
: It determines which method is called when multiple parents define the same method. It also affects super() . : class Foo: def __init__(self): self
class SingletonMeta(type): _instances = {} def __call__(cls, *args, **kwargs): if cls not in cls._instances: cls._instances[cls] = super().__call__(*args, **kwargs) return cls._instances[cls] class Database(metaclass=SingletonMeta): pass python 3 deep dive part 4 oop high quality
class Singleton: _instance = None def __new__(cls, *args, **kwargs): if cls._instance is None: cls._instance = super().__new__(cls) return cls._instance s1 = Singleton() s2 = Singleton() print(s1 is s2) # True