':return: This URL concatenated with the "other" string.'

def __add__(self, other):

    if (not isinstance(other, basestring)):
        msg = "cannot    concatenate    '%s'    and    '%s'    objects"
        msg = (msg % (other.__class__.__name__, self.__class__.__name__))
        raise TypeError(msg)
    return (self.url_string + other)
