input: from typing import List
  
  def reverse_words(sentence: str) -> str:
      """ Reverse the order of words in a given sentence, keeping the order of characters in each word unchanged.
      >>> reverse_words('This is a sentence.')
      'sentence. a is This'
      >>> reverse_words('How are you doing today?')
      'today? doing you are How'
      """
      
      words = sentence.split(" ")
      reversed_words = []
      for word in words:
          reversed_words.insert(0, word)
      return ' '.join(reversed_words)
output:     words = sentence.split(" ")
      reversed_words = []
      for word in words:
          reversed_words.insert(0, word)
      return ' '.join(reversed_words)