(v)
Returns True if v is a valid object that can be stored by this
        class.
Returns True if v is a valid object that can be stored by this
        class.
Returns True if v is a valid object that can be stored by this class .
def is_valid(v):
        """Returns True if v is a valid object that can be stored by this
        class.
        """

        raise NotImplementedError
def is_valid ( v ) : raise NotImplementedError