code: def get_edge_index(mol):
      # construct edge (bond) index
      src, dest = [], []
      for bond in mol.GetBonds():
          # add edge list considering a directed graph
          start, end = bond.GetBeginAtomIdx(), bond.GetEndAtomIdx()
          src += [start, end]
          dest += [end, start]
      return np.asarray([src, dest], dtype=int)
  
imports: from deepchem.feat.base_classes import MolecularFeaturizer
  from deepchem.feat import MolGraphConvFeaturizer
  from rdkit import Chem
  import unittest
  import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: get_edge_index(mol) and returns: np