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. The function should take a string as input and return the modified string.
  
  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("Python is fun") == "fun is Python"
  assert reverse_words("") == ""
  assert reverse_words("SingleWord") == "SingleWord"
  assert reverse_words("One Two Three Four") == "Four Three Two One"
output: def reverse_words(string):
    words = string.split(" ")
    reversed_words = []
    for word in words:
      reversed_words.insert(0, word)
    return ' '.join(reversed_words)