docs: def _setup_direct_converter(self, converter):
          '''
          Given a converter, set up the direct_output routes for conversions,
          which is used for transcoding between similar datatypes.
          '''
          inputs = (
              converter.direct_inputs
              if hasattr(converter, 'direct_inputs')
              else converter.inputs
          )
          for in_ in inputs:
              for out in converter.direct_outputs:
                  self.direct_converters[(in_, out)] = converter