You can find the nth occurrence of a substring in a string by splitting at the substring with max n+1 splits. If the resulting list has a size greater than n+1, it means that the substring occurs more than n times. Its index can be found by a simple formula, length of the original string - length of last splitted part - length of the substring.
def findnth(string, substring, n): parts = string.split(substring, n + 1) if len(parts) <= n + 1: return -1 return len(string) - len(parts[-1]) - len(substring) findnth('foobarfobar akfjfoobar afskjdf foobar', 'foobar', 2)
This would give the output:
The n in this starts from 0. It is quite trivial to change that.