code: def node_theta(nodelist, node):
      
      assert len(nodelist) > 0, "nodelist must be a list of items."
      assert node in nodelist, "node must be inside nodelist."
  
      i = nodelist.index(node)
      theta = -np.pi + i * 2 * np.pi / len(nodelist)
  
      return theta
docs: Maps node to Angle.
  
      :param nodelist: Nodelist from the graph.
      :type nodelist: list.
      :param node: The node of interest. Must be in the nodelist.
      :returns: theta -- the angle of the node in radians.