class Chain(object):

    def __init__(self, path=''):
        self._path = path

    def __getattr__(self, path):
        return Chain('%s/%s' % (self._path, path))

    def __str__(self):
        return self._path

    __repr__ = __str__

>>> Chain().status.user.timeline.list
'/status/user/timeline/list'   #怎么得出的这个结果？

1，Chain() 实例化，执行init, path默认为空， str返回空

2，Chain().status ,实例调用属性不存在，执行getattr方法。获取Chain(‘/status’)覆盖Chain，str返回/status

3，Chain().status.user.执行getatter. 获取Chain(‘/status/user’), str返回/status/user’

.....最后str返回/status/user/timeline/list

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Chain().users('michael').repos  #这种调用方法的结果如何理解？
同理。只不过('michael')调用会找call()方法。结果，过程也是一样的
def __call__(self, path):
     return Chain('%s/%s' % (self._path, path))
def __getattr__(self, path):
     return Chain('%s/%s' % (self._path, path))