code: def __nt_relpath(path, start=os.curdir):
      
  
      if not path: raise ValueError("no path specified")
  
      start_list = os.path.abspath(start).split(os.sep)
      path_list = os.path.abspath(path).split(os.sep)
      if start_list[0].lower() != path_list[0].lower():
          unc_path, rest = os.path.splitunc(path)
          unc_start, rest = os.path.splitunc(start)
          if bool(unc_path) ^ bool(unc_start):
              raise ValueError("Cannot mix UNC and non-UNC paths (%s and %s)" \
                               % (path, start))
          else: raise ValueError("path is on drive %s, start on drive %s" \
                                 % (path_list[0], start_list[0]))
      # Work out how much of the filepath is shared by start and path.
      for i in range(min(len(start_list), len(path_list))):
          if start_list[i].lower() != path_list[i].lower():
              break
          else: i += 1
          pass
  
      rel_list = [os.pardir] * (len(start_list)-i) + path_list[i:]
      if not rel_list: return os.curdir
      return os.path.join(*rel_list)
docs: Return a relative version of a path