How to find the index of the nth ocurrence of a character in a string

Question

"/home/hernan/PycharmProjects/test1/tensor.py".find('e')   #Returns 4
"/home/hernan/PycharmProjects/test1/tensor.py".find('e',2) #Also 4
"/home/hernan/PycharmProjects/test1/tensor.py".find('e',3) #Also 4

I would like something like:

"/home/hernan/PycharmProjects/test1/tensor.py".find('e',2) #Returns 7
"/home/hernan/PycharmProjects/test1/tensor.py".find('e',3) #Returns 14

Those are the second and third ocurrences of 'e'.

Any built-in function in Python 3.x to get the index of the nth ocurrence of a character in a string?

i Could do that, but Im looking for a built-in function in Python. I've specified my answer so that it is clearer. — Hernan, May 06 '19 at 23:38
I see. There's a very comprehensive question and answers on Stackoverflow (https://stackoverflow.com/questions/1883980/find-the-nth-occurrence-of-substring-in-a-string). However I don't believe there's any built-in function that can achieve this. — Philip Tzou, May 06 '19 at 23:42

Philip Tzou · Answer 1 · 2019-05-06T23:45:01.473

1

Why not just use a for-loop?

def find_nth(text, sub, nth):
    start = -1
    for i in range(nth):
        start = text.find(sub, start + 1)
        if start == -1:
            break
    return start


find_nth("/home/hernan/PycharmProjects/test1/tensor.py", 'e', 2) # returns 7
find_nth("/home/hernan/PycharmProjects/test1/tensor.py", 'e', 3) # returns 24

edited May 06 '19 at 23:45

answered May 06 '19 at 23:39

Philip Tzou

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score 0 · Answer 2 · answered May 06 '19 at 23:43

The second argument in the str.find function is to indicate the start index. Not the index of the occurrence to start looking from. 'find a char'.find('a', 3) is equivalent to 'find a char'[3:].find('a') + 3 (sort of; not dealing with the search string not being present in the full string that it's being searched for in). You'll have to write your own function for this.

def search(full, toFind, occ):
    ret = 0
    while occ:
        ret = full.find( toFind, ret ) + 1
        occ -= 0
        if ret == -1:
            return -1
    return ret

How to find the index of the nth ocurrence of a character in a string

Any built-in function in Python 3.x to get the index of the nth ocurrence of a character in a string?

2 Answers2