code: def relpath(path, start):
      
      path_items = path_list(path)
      start_items = path_list(start)
  
      # Find common parts of path.
      common = []
      for pth, stt in zip(path_items, start_items):
          if pth != stt:
              break
          common.append(pth)
  
      # Shared parts index in both lists.
      common_ind = len(common)
      parent_num = len(start_items) - common_ind
  
      # Start with parent traversal and add relative parts.
      rel_items = [PARENT] * parent_num + path_items[common_ind:]
      return path_join(*rel_items)
docs: Get relative path to start.
  
      Note: Modeled after python2.6 :meth:`os.path.relpath`.