使用属性装饰器

@property 装饰器可用于在类中定义类似属性的方法。这可能有用的一个例子是当暴露可能需要初始（昂贵）查找和之后的简单检索的信息时。

鉴于一些模块 foobar.py：

class Foo(object):
    def __init__(self):
        self.__bar = None

    @property
    def bar(self):
        if self.__bar is None:
            self.__bar = some_expensive_lookup_operation()
        return self.__bar

然后

>>> from foobar import Foo
>>> foo = Foo()
>>> print(foo.bar)  # This will take some time since bar is None after initialization
42
>>> print(foo.bar)  # This is much faster since bar has a value now
42