Docserver: there is only one.

chrome/common/extensions/docs/server2/object_store.py

 # Copyright (c) 2012 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.
 
 from future import Future
 
 class _SingleGetFuture(object):
   def __init__(self, multi_get, key):
     self._future = multi_get
     self._key = key
 
   def Get(self):
     return self._future.Get().get(self._key)
 
 class ObjectStore(object):
   '''A class for caching picklable objects.
   '''
   def Get(self, key):
     '''Gets a |Future| with the value of |key| in the object store, or None
     if |key| is not in the object store.
     '''
     return Future(delegate=_SingleGetFuture(self.GetMulti([key]), key))
 
   def GetMulti(self, keys):
     '''Gets a |Future| with values mapped to |keys| from the object store, with
     any keys not in the object store omitted.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def Set(self, key, value):
     '''Sets key -> value in the object store.
     '''
     self.SetMulti({ key: value })
 
   def SetMulti(self, items):
     '''Atomically sets the mapping of keys to values in the object store.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def Del(self, key):
     '''Deletes a key from the object store.
     '''
     self.DelMulti([key])
 
   def DelMulti(self, keys):
     '''Deletes |keys| from the object store.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)