input: Write a function to identify the longest word in a given sentence. If there is a tie for the longest word, return the first one encountered. If the sentence is empty, return an empty string.
  def find_longest_word(sentence):
      words = sentence.split()
      # initialise longest_word variable with 0
      longest_word = 0
      for word in words:
          if len(word) > longest_word:
              longest_word = len(word)
              longest_word_str = word
      return longest_word_str if longest_word > 0 else ""
  
  assert find_longest_word("The rain in Spain stays mainly in the plain.") == "mainly"
  assert find_longest_word("The quick brown fox jumps over the lazy dog.") == "quick"
  assert find_longest_word("This sentence has no spaces.") == "This"
  assert find_longest_word("") == ""
output: def find_longest_word(sentence):
      words = sentence.split()
      if not words:
          return ""
      longest_word = words[0]
      for word in words:
          if len(word) > len(longest_word):
              longest_word = word
      return longest_word