如何列出一个子类的所有实例？

class ParentClass:
    pass

class SubClass(ParentClass):
    pass

# 创建子类的实例
sub_instance1 = SubClass()
sub_instance2 = SubClass()

# 创建父类的实例
parent_instance = ParentClass()

# 列出子类的所有实例
def list_subclass_instances(subclass):
    instances = []
    for instance in vars().values():
        if isinstance(instance, subclass):
            instances.append(instance)
    return instances

sub_instances = list_subclass_instances(SubClass)
print(sub_instances)