docs: def link(self, stream_instance):
          """Set my input stream"""
          if isinstance(stream_instance, collections.Iterable):
              self.input_stream = stream_instance
          elif getattr(stream_instance, 'output_stream', None):
              self.input_stream = stream_instance.output_stream
          else:
              raise RuntimeError('Calling link() with unknown instance type %s' % type(stream_instance))