让属性具备惰性求值的能力

"""
属性惰性求值
这里介入描述符就可以实现
"""


class LazyProperty:
    def __init__(self, func):
        self.func = func

    def __get__(self, instance, owner):
        if instance is None:
            return self
        value = self.func(instance)
        setattr(instance, self.func.__name__, value)
        return value


class Valley:

    @LazyProperty
    def age(self):
        print("shi_xiao_gu_a")
        return 2 * 13


v = Valley()
print(v.age)
print(v.age)