我如何返回到我的代碼的開始/有一個嵌套循環？

Question

我想我的代碼運行，以便如果條件不符合（在if循環中）它將返回到代碼的開頭，要求用戶輸入另一個句子。我如何添加這個嵌套循環（如果這就是它所謂的）？

sentence = input("Please input a sentence: ") 
word = input("Please input a word: ") 
sentence = sentence.lower() 
word = word.lower() 
wordlist = sentence.split(' ') 
print ("Your word, {0}, is in positions:".format (word)) 
for position,w in enumerate(wordlist): 
    if w == word: 
     print("{0}".format(position+1)) 

Answer 1

只要做到：

while True: 
    sentence = input("Please input a sentence: ") 
    if sentence.lower() == "quit": break 
    word = input("Please input a word: ") 
    sentence = sentence.lower() 
    word = word.lower() 
    wordlist = sentence.split(' ') 
    print ("Your word, {0}, is in positions:".format (word)) 
    for position,w in enumerate(wordlist): 
     if w == word: 
      print("{0}".format(position+1)) 

Answer 2

你可以把周圍的代碼和break或continue一個while迴路根據輸入：

while True: 
    sentence = input("Please input a sentence: ") 
    if bad(sentence): # replace with actual condition 
     continue 
    ... 
    for position, w in enumerate(wordlist): 
     ... 
    break