code: def circular_layout(nodes):
      
      N = len(nodes)
      if not N:
          return ([], [], [])
      circ = np.pi/N*np.arange(N)*2
      x = np.cos(circ)
      y = np.sin(circ)
      return (x, y, nodes)
docs: Lay out nodes on a circle and add node index.