Python ValueError:未找到子字符串-定义单词时出错

我正在尝试制作一个程序，当你输入一个句子时，它会要求你搜索一个单词，它会告诉你这个句子出现在哪里 代码如下：

loop=1
while loop:
    sent = str(input("Please type a sentence without punctuation:"))
    lows = sent.lower()
    word = str(input("please enter a word you would want me to locate:"))
    if word:
        pos = sent.index(word)
        pos = pos + 1
        print(word, "appears at the number:",pos,"in the sentence.")
    else:
        print ("this word isnt in the sentence, try again")
        loop + 1
        loop = int(input("Do you want to end ? (yes = 0); no = 1):"))

它似乎工作良好，直到我键入错误例如你好，我的名字是威尔 我想找到的单词是它，而不是“对不起，这句话中没有出现”，而是事实上的ValueError:substring not found

---

我真的不知道如何解决这个问题，需要帮助。

看看

str.index

和

str.find

在未找到子字符串时会发生什么

>>> help(str.find)
Help on method_descriptor:

find(...)
    S.find(sub[, start[, end]]) -> int

    Return the lowest index in S where substring sub is found,
    such that sub is contained within S[start:end].  Optional
    arguments start and end are interpreted as in slice notation.

    Return -1 on failure.

>>> help(str.index)
Help on method_descriptor:

index(...)
    S.index(sub[, start[, end]]) -> int

    Like S.find() but raise ValueError when the substring is not found.

---

对于

str.index

您需要一个

try/except

语句来处理无效输入。对于

str.find

if语句，检查返回值是否不是

-1

就足够了。

与您的方法稍有不同

def findword():
    my_string = input("Enter string: ")
    my_list = my_string.split(' ')
    my_word = input("Enter search word: ")
    for i in range(len(my_list)):
        if my_word in my_list[i]:
            print(my_word," found at index ", i)
            break
    else:
        print("word not found")

def main():
    while 1:
        findword()
        will_continue = int(input("continue yes = 0, no = 1; your value => "))
        if(will_continue == 0):
            findword()
        else:
            print("goodbye")
            break;
main()

---

将索引调用封装在

try/except ValueError

语句中。这很容易理解。