code: def preprocess(graph):
      global n_node_feats
  
      # add reverse edges
      srcs, dsts = graph.all_edges()
      graph.add_edges(dsts, srcs)
  
      # add self-loop
      print(f"Total edges before adding self-loop {graph.num_edges()}")
      graph = graph.remove_self_loop().add_self_loop()
      print(f"Total edges after adding self-loop {graph.num_edges()}")
  
      graph.create_formats_()
  
      return graph
  
file_path: dgl/examples/pytorch/ogb/ogbn-arxiv/correct_and_smooth.py
imports: import argparse
  import glob
  import numpy
  import torch
  import torch.nn.functional
  from dgl import function
  from ogb.nodeproppred import DglNodePropPredDataset, Evaluator
label_desc: Use image node_id 2 for calling a global function with example usage: preprocess(graph) and returns: graph