input: 
  def find_longest_word(sentence: str) -> str:
      """ Finds and returns the longest word in the given sentence.
      >>> find_longest_word("The rain in Spain stays mainly in the plain.")
      'mainly'
      """
      words = sentence.split()
      longest_word_str = ""
      for word in words:
          if len(word) > len(longest_word_str):
              longest_word_str = word
      return longest_word_str
  
output:     words = sentence.split()
      longest_word_str = ""
      for word in words:
          if len(word) > len(longest_word_str):
              longest_word_str = word
      return longest_word_str