code: def read_d1_letter(fin_txt):
      
      go2letter = {}
      re_goid = re.compile(r"(GO:\d{7})")
      with open(fin_txt) as ifstrm:
          for line in ifstrm:
              mtch = re_goid.search(line)
              if mtch and line[:1] != ' ':
                  # Alias is expected to be the first character
                  go2letter[mtch.group(1)] = line[:1]
      return go2letter
docs: Reads letter aliases from a text file created by GoDepth1LettersWr.