text: # Copyright (c) 2013 Rackspace, Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #    http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
  # implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  """
  Base utilities to build API operation managers.
  """
  import uuid
  
  
  def filter_null_keys(dictionary):
      return dict(((k, v) for k, v in dictionary.items() if v is not None))
  
  
  def validate_ref(ref, entity):
      """Verifies that there is a real uuid at the end of the uri
  
      :return: Returns True for easier testing
      :raises ValueError: If it cannot correctly parse the uuid in the ref.
      """
      try:
          _, entity_uuid = ref.rstrip('/').rsplit('/', 1)
          uuid.UUID(entity_uuid)
      except:
          raise ValueError('{0} incorrectly specified.'.format(entity))
  
      return True
  
  
  class ImmutableException(Exception):
      def __init__(self, attribute=None):
          message = "This object is immutable!"
          super(ImmutableException, self).__init__(message)
  
  
  class BaseEntityManager(object):
      def __init__(self, api, entity):
          self._api = api
          self._entity = entity
  
      def total(self):
          """
          Returns the total number of entities stored in Barbican.
          """
          params = {'limit': 0, 'offset': 0}
          resp = self._api.get(self._entity, params=params)
  
          return resp['total']
  