| # Copyright 2014 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| MERGE_FAILURE_REASON = ( |
| 'Merging values containing a None value results in a None value.') |
| |
| class NoneValueMissingReason(Exception): |
| pass |
| |
| class ValueMustHaveNoneValue(Exception): |
| pass |
| |
| def ValidateNoneValueReason(value, none_value_reason): |
| """Ensures that the none_value_reason is appropriate for the given value. |
| |
| There is a logical equality between having a value of None and having a |
| reason for being None. That is to say, value is None if and only if |
| none_value_reason is a string. |
| """ |
| if value is None and not isinstance(none_value_reason, basestring): |
| raise NoneValueMissingReason() |
| if value is not None and none_value_reason is not None: |
| raise ValueMustHaveNoneValue() |
