input: 
  def replace_word(sentence: str, old_word: str, new_word: str) -> str:
      """ Replace a given word in the sentence with another word.
      >>> replace_word("I love walking on the beach", "walking", "swimming")
      'I love swimming on the beach'
      >>> replace_word("Python is fun", "fun", "amazing")
      'Python is amazing'
      """
      return sentence.replace(old_word, new_word)
  
output:     return sentence.replace(old_word, new_word)