Python ValueError: substring not found - Error defining a word

Question

I'm trying to make a program that when you type a sentence it asks for a word to search and it will tell you where in the sentence it sentence occurs the code is as follows:

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):"))

It seems to work fine until I type it incorrectly eg hello my name is Will and the word I want to find is it instead of "sorry this doesn't occur in the sentence" but infact ValueError : substring not found

I honestly dont know how to fix this and need help please.

wrap your index call in a try/except ValueError statement. — Jean-François Fabre
– Jean-François Fabre ♦, Commented Jan 12, 2017 at 13:04

Steven Summers · Accepted Answer · 2017-01-12 13:06:48Z

1

Have a look at what happens for str.index and str.find when substring is not found.

>>> 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.

For str.index you will need a try/except statement to handle invalid input. For str.find an if statement checking if the return value isn't -1 will suffice.

answered Jan 12, 2017 at 13:06

Steven Summers

5,4242 gold badges24 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Maddy · Accepted Answer · 2017-01-12 13:36:02Z

1

A little different from your approach.

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()

edited Jan 12, 2017 at 13:36

answered Jan 12, 2017 at 13:11

Maddy

2,0905 gold badges30 silver badges64 bronze badges

1 Comment

Jeff Benister Over a year ago

this was easy to understand.

Collectives™ on Stack Overflow

Python ValueError: substring not found - Error defining a word

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related