input: Write a python function to extract distinct words from a sentence.
  assert distinct_words("this is a test this is only a test") == ["this", "is", "a", "test", "only"]
  assert distinct_words("hello world hello") == ["hello", "world"]
  assert distinct_words("python python python") == ["python"]
  assert distinct_words("unique words are unique") == ["unique", "words", "are"]
output: def distinct_words(sentence):
      return list(dict.fromkeys(sentence.split()))