def pretty_const(self, index):
        """
        a tuple of the pretty type and val, or (None, None) for invalid
        indexes (such as the second part of a long or double value)
        """

        t, v = self.consts[index]
        if not t:
            return None, None
        else:
            return _pretty_const_type_val(t, v)
a tuple of the pretty type and val, or (None, None) for invalid
        indexes (such as the second part of a long or double value)