comparing strings in python

Question

def find_last(search, target):
    for index, character in reversed(list(enumerate(search))):
        if character in target:
            return index
        else:
            return -1

suppose search="aaaaa" and target="aa", output should=3, not 4. I am trying to get the last position where the two strings compare

Shashank · Accepted Answer · 2015-04-07 05:24:03Z

3

Currently what you're doing is comparing each character from the search string in reverse order and seeing if it's in target. If it is, you prematurely return the wrong index.

Instead, I would recommend using the str.rfind method:

>>> 'aaaaa'.rfind('aa')
3

str.rfind is basically the same thing as the str.index method except it searches for the first needle from the right of the haystack.

Edit: In order to treat empty needles as being present at the rightmost index, you can use the following return expression:

def find_last(search, target):
        return target and search.rfind(target) or len(search)

edited Apr 7, 2015 at 5:24

answered Apr 7, 2015 at 4:57

Shashank

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2 Comments

Spencer Josephs Over a year ago

but if i have a string "22222222", and target="", out put should be 9, not -1. but rfind does not put this scenario into consideration

Shashank Over a year ago

@SpencerJosephs Ah, I see. I've edited the answer to make it return the length of the search string if the target is an empty string.

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