code: def get_inverse_etype(etype):
      fields = etype.split("2")
      if len(fields) == 3:
          src, etype, dst = fields
          r_etype = "2".join([dst, etype, src])
      else:
          r_etype = "2".join([fields[1], fields[0]])
      return r_etype
  
imports: import sys
  import datetime
  import os
  import yaml
  import random
  import shutil
  import six
  import warnings
  import glob
  from collections import defaultdict
  from pgl.utils.logger import log
label_desc: Use image node_id 4 for calling a global function with example usage: get_inverse_etype(etype) and returns: r_etype