code: def pop_configuration(self):
          
          if len(self.__configurations) == 1:
              raise IndexError('Can not pop the last configuration from the '
                               'stack of configurations.')
          self.__configurations.pop()
          self.__mapped_attr_cache.clear()
docs: Pushes the currently active configuration from the stack of
          configurations managed by this mapping.
  
          :raises IndexError: If there is only one configuration in the stack.