def to_params(self):
        """
        Convert the instance dictionary into a sorted list of pairs
        (name, valrepr) where valrepr is the string representation of
        the underlying value.
        """
        dic = self.__dict__
        return [(k, repr(dic[k])) for k in sorted(dic)
                if not k.startswith('_')]
Convert the instance dictionary into a sorted list of pairs
        (name, valrepr) where valrepr is the string representation of
        the underlying value.