'The user\'s predicates are consulted first, then the default predicates.'

def _GetPredicate(self, pred_str):

    (predicate, args, func_type) = self.predicates.LookupWithType(pred_str)
    if predicate:
        return (predicate, args, func_type)
    else:
        raise BadPredicate(('%r    is    not    a    valid    predicate' % pred_str))
