code: def _load_bond_length_data():
      
      with open(os.path.join(os.path.dirname(__file__),
                             "bond_lengths.json")) as f:
          data = collections.defaultdict(dict)
          for row in json.load(f):
              els = sorted(row['elements'])
              data[tuple(els)][row['bond_order']] = row['length']
          return data
docs: Loads bond length data from json file