docs: def normalizeISBN(isbn):
      """
      >>> normalizeISBN('978800105473-4')
      '978-80-01-05473-4'
  
      >>> normalizeISBN('80978800105473-4')
      '80978800105473-4'
  
      >>> normalizeISBN('988800105473-4')
      '988800105473-4'
  
      >>> normalizeISBN('978-80-254-94677')
      '978-80-254-9467-7'
      """
      try:
          return isbnlib.mask(isbnlib.canonical(isbn))
      except isbnlib.NotValidISBNError:
          return isbn