python如何将一个类的实例变量传递给另一个类？

class ClassA:
    def __init__(self, value):
        self.value = value

class ClassB:
    def __init__(self, instance):
        self.instance = instance

a = ClassA(10)
b = ClassB(a)

class ClassA:
    def __init__(self, value):
        self.value = value

class ClassB:
    def set_instance(self, instance):
        self.instance = instance

a = ClassA(10)
b = ClassB()
b.set_instance(a)

class ClassA:
    def __init__(self, value):
        self.value = value

class ClassB:
    instance = None

a = ClassA(10)
b = ClassB()
b.instance = a