input: Write a function to reverse the order of words in a sentence but keep the order of the characters in each word the same.
  
  def reverse_words(string):
    words = string.split(" ")
    reversed_words = []
    for word in words:
      reversed_words.insert(0, word)
    return ' '.join(reversed_words)
  
  assert reverse_words("This is a sentence.") == "sentence. a is This"
  assert reverse_words("Hello world") == "world Hello"
  assert reverse_words("SingleWord") == "SingleWord"
  assert reverse_words("") == ""
  assert reverse_words("Sentence with multiple words") == "words multiple with Sentence"
output: def reverse_words(string):
    words = string.split(" ")
    reversed_words = words[::-1]
    return ' '.join(reversed_words)