CODEWITHSUNDEEP
pythonpython-3.x
chuddles
chuddles

Reputation: 19

Python: Finding the position of the first occurring difference between 2 strings. (Unequal lengths)

I have been trying to solve this past final exam question. I think I am getting close, but due to the unequal lengths of the two strings, I am getting an index out of range error which i can't figure out...

How would you try solve this question? How can I solve the IndexError?

Thank you in advance :D 

def print_first_difference(string1, string2):
    """ Solving the first difference between 2 words, and print the position. """
    for letter in range(len(string1)):
        if string1[letter] != string2[letter]:
            print("Strings differ at postion {}".format(letter + 1))
            break
    else:
        print("Strings are identical")


print_first_difference("abcd", "abde")  
print_first_difference("abcdef", "abcdef")  
print_first_difference("abcdef", "abc") 
print_first_difference("abc", "abcdef") 

Output:
Strings differ at postion 3
Strings are identical
IndexError: string index out of range

Upvotes: 1

Views: 1783

Answers (2)

Jivan
Jivan

Reputation: 23098

Encapsulate your test in a try/catch in case of IndexError, which means that the second string is shorter than the first one, which means the two strings differ.

for letter in range(len(string1)):
    try:
        if string1[letter] != string2[letter]:
            print("Strings differ at postion {}".format(letter + 1))
            break
    except IndexError:
            print("Strings differ at postion {}".format(letter + 1))
            break

Edit: have you thought about the case where string1 is shorter than string2? I think your algorithm will assume both strings are identical.

Upvotes: 3

ádi
ádi

Reputation: 31

My solution would be:

def print_first_difference(string1, string2):
    aggr_strings = zip(string1, string2)
    for index, tup in enumerate(aggr_strings):
        if tup[0] != tup[1]:
            print("Strings differ at position " + str(index))
            break
    else:
        if len(aggr_strings) != len(max(string1, string2)):
            print("Strings differ at position " + str(len(min(string1, string2))))
        else:
            print("Strings are identical")

Upvotes: 1

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