Optinal

optional.py

class Optional:
    
    """
    >>> class User:
    ...     def __init__(self, friend_a, friend_b):
    ...         self.friend_a = friend_a
    ...         self.friend_b = friend_b
    ...
    ...     def calc(self):
    ...         return 5
    ...
    >>> user_a = User(None, None)
    >>> user_b = User(user_a, None)
    >>> Optial(user_b).friend_a.calc().v
    5
    >>> Optial(user_b).friend_a.calc().v
    None
    >>> Optial(user_a).friend_b.v
    None
    """

    def __init__(self, value):
        self.v = value
    
    def __call__(self, *args, **kw):
        if self.v is None:
            return self.__class__(None)
        return self.__class__(self.v(*args, **kw))
    
    def __getattr__(self, item):
        if self.v is None:
            return self.__class__(None)
        return self.__class__(getattr(self.v, item))