input: 
  def find_longest_word(sentence: str) -> str:
      """
      Identifies the longest word in a given sentence.
      >>> find_longest_word("The rain in Spain stays mainly in the plain.")
      'mainly'
      """
      words = sentence.split()
      # initialise longest_word variable with empty string
      longest_word = ''
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word
  
output:     words = sentence.split()
      # initialise longest_word variable with empty string
      longest_word = ''
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word