code: def encode(g, top=None, cls=PENMANCodec, **kwargs):
      
      codec = cls(**kwargs)
      return codec.encode(g, top=top)
docs: Serialize the graph *g* from *top* to PENMAN notation.
  
      Args:
          g: the Graph object
          top: the node identifier for the top of the serialized graph; if
              unset, the original top of *g* is used
          cls: serialization codec class
          kwargs: keyword arguments passed to the constructor of *cls*
      Returns:
          the PENMAN-serialized string of the Graph *g*
      Example:
  
          >>> encode(Graph([('h', 'instance', 'hi')]))
          (h / hi)