code: def get_chunk(self, obj):
          
          if self._chunkattr is None:
              return
          a = attrgetter(self._chunkattr)(obj)
          if a is None:
              return
          s = self._chunkformat % a
          return s
docs: Return the chunkattr of obj formatted with the chunkfomat specified in the constructor
          If the attr is None then ``None`` is returned not the string ``\'None\'``.
  
          :param obj: the fileinfo with information.
          :type obj: :class:`FileInfo`
          :returns: the chunk or None
          :rtype: str|None
          :raises: None