code: def _compare_by_version(path1, path2):
      
      if path1.source == path2.source:
          if path1.source_version_num > path2.source_version_num:
              return path1
          else:
              return path2
      return None
docs: Returns the current/latest learned path.
  
      Checks if given paths are from same source/peer and then compares their
      version number to determine which path is received later. If paths are from
      different source/peer return None.