code: def get_decoder(self, content_type):
          
          if content_type in self._decoders:
              return self._decoders[content_type]
          else:
              return self._client.get_decoder(content_type)
docs: Get the decoding function for the provided content type for
          this bucket.
  
          :param content_type: the requested media type
          :type content_type: str
          :rtype: function