我们将做一些关于函数和变量的练习，以确认你真正掌握了这些知识。这节练习对你来说可以说是一本道：写程序，逐行研究，弄懂它。
不过这节练习还是有些不同，你不需要运行它，取而代之，你需要将它导入到 python 里通过自己执行函数的方式运行。
1 def break_words(stuff): 2 """This function will break up words for us.""" 3 words = stuff.split(' ') 4 return words 5 6 def sort_words(words): 7 """Sorts the words.""" 8 return sorted(words) 9 10 def print_first_word(words): 11 """Prints the first word after popping it off.""" 12 word = words.pop(0) 13 print word 14 15 def print_last_word(words): 16 """Prints the last word after popping it off.""" 17 word = words.pop(-1) 18 print word 19 20 def sort_sentence(sentence): 21 """Takes in a full sentence and returns the sorted words.""" 22 words = break_words(sentence) 23 return sort_words(words) 24 25 def print_first_and_last(sentence): 26 """Prints the first and last words of the sentence.""" 27 words = break_words(sentence) 28 print_first_word(words) 29 print_last_word(words) 30 31 def print_first_and_last_sorted(sentence): 32 """Sorts the words then prints the first and last one.""" 33 words = sort_sentence(sentence) 34 print_first_word(words) 35 print_last_word(words)