def suitability_as_key(self, key_name):
        """
        Returns: (result, key_type)
        ``result`` is True, False, or 'absent' or 'partial' (both still usable)
        ``key_type`` is ``int`` for integer keys or ``str`` for hash keys

        """
        pk_values = all_values_for(self, key_name)
        if not pk_values:
            return ('absent', int)  # could still use it
        key_type = type(th.best_coercable(pk_values))
        num_unique_values = len(set(pk_values))
        if num_unique_values < len(pk_values):
            return (False, None)     # non-unique
        if num_unique_values == len(self):
            return (True, key_type)  # perfect!
        return ('partial', key_type)
Returns: (result, key_type)
        ``result`` is True, False, or 'absent' or 'partial' (both still usable)
        ``key_type`` is ``int`` for integer keys or ``str`` for hash keys