code: def _find_first_of(line, substrings):
      
      starts = ((line.find(i), i) for i in substrings)
      found = [(i, sub) for i, sub in starts if i != -1]
      if found:
          return min(found)
      else:
          return -1, None
docs: Find earliest occurrence of one of substrings in line.
  
      Returns pair of index and found substring, or (-1, None)
      if no occurrences of any of substrings were found in line.