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)) 
         

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