Python | Ways to find nth occurrence of substring in a string

Given a string and a substring, write a Python program to find the n^th occurrence of the string. Let’s discuss a few methods to solve the given task.

Method #1: Using re

# Python code to demonstrate
# to find nth occurrence of substring

import re

# Initialising values
ini_str = "abababababab"
substr = "ab"
occurrence = 4


# Finding nth occurrence of substring
inilist = [m.start() for m in re.finditer(r"ab", ini_str)]
if len(inilist)>= 4:

    # Printing result
    print ("Nth occurrence of substring at", inilist[occurrence-1])
else:
    print ("No {} occurrence of substring lies in given string".format(occurrence))

Method #2: Using find() method

# Python code to demonstrate
# to find nth occurrence of substring

# Initialising values
ini_str = "abababababab"
sub_str = "ab"
occurrence = 4


# Finding nth occurrence of substring
val = -1
for i in range(0, occurrence):
    val = ini_str.find(sub_str, val + 1)

# Printing nth occurrence
print ("Nth occurrence is at", val)

Method #3: Using startswith() and list comprehension

# Python code to demonstrate
# to find nth occurrence of substring

# Initialising values
ini_str = "abababababab"
substr = "ab"
occurrence = 4


# Finding nth occurrence of substring
inilist = [i for i in range(0, len(ini_str))
            if ini_str[i:].startswith(substr)]

if len(inilist)>= 4:

    # Printing result
    print ("Nth occurrence of substring at", inilist[occurrence-1])
else:
    print ("No {} occurrence of substring lies in given string".format(occurrence))