Use luci-config for infrequently changing settings, part 2.

appengine/components/components/datastore_utils/config.py

 # Copyright 2014 The Swarming Authors. All rights reserved.
 # Use of this source code is governed by the Apache v2.0 license that can be
 # found in the LICENSE file.
 
 """Versioned singleton entity with global application configuration.
 
 Example usage:
   from components.datastore_utils import config
 
   class MyConfig(config.GlobalConfig):
@@ skipping 15 matching lines @@
 
 Advantages over regular ndb.Entity with predefined key:
   1. All changes are logged (see datastore_utils.store_new_version).
   2. In-memory process-wide cache.
 
 TODO: Get rid of components.auth dependency. It creates circular import between
 components.auth and components.datastore_utils. components.datastore_utils is on
 "lower" level than components.auth and must not depend on it.
 """
 
+# Pylint fails to recognize that ndb.Model.key is defined in ndb.Model.
+# pylint: disable=attribute-defined-outside-init
+
 from google.appengine.ext import ndb
 
 from components import auth
 from components import datastore_utils
 from components import utils
 
 
 class GlobalConfig(ndb.Model):
   """Singleton entity with the global configuration of the service.
 
@@ skipping 74 matching lines @@
 
   _config_fetcher = None
 
   @classmethod
   def _get_root_model(cls):
     return datastore_utils.get_versioned_root_model('%sRoot' % cls.__name__)
 
   @classmethod
   def _get_root_key(cls):
     return ndb.Key(cls._get_root_model(), 1)