为什么我按照书上的运行一直显示这个

Question

def break_words(stuff):
	"""This function will break up words for us."""
	words = stuff.split(' ')
	return words
	
def sort_words(words):
	"""Sorts the words."""
	return sorted(words)
	
def print_first_word(words):
	"""Prints the first word after popping it off."""
	word = word.pop(-1)
	print word
	
def print_last_word(words):
	"""Prints the last word after popping it off ."""
	word = wor.pop(-1)
	print word
	
def sort_sentence(sentence):
	"""Prints in a full sentence and return the sorted words."""
	words = break_words(sentence)
	return sort_words(word)
	
def print_first_and_last(sentence):
	"""Prints the first and last words of the sentence."""
	words = break_words(sentence)
	print_first_word(words)
	print_last_word(words)
	
def print_first_and_last_sorted(sentence):
	"""Sorts the words then prints the first and last one."""
	words = sort_sentence(sentence)
	print_first_word(words)
	print_last_word(words)

Answer 1

注意import