code: def group_theta(node_length, node_idx):
      
      theta = -np.pi + node_idx * 2 * np.pi / node_length
      return theta
docs: Returns an angle corresponding to a node of interest.
  
      Intended to be used for placing node group labels at the correct spot.
  
      :param float node_length: total number of nodes in the graph.
      :param int node_idx: the index of the node of interest.
      :returns: theta -- the angle of the node of interest in radians.