Skip to content
Related Articles

Related Articles

Improve Article

Python | Get the starting index for all occurrences of given substring

  • Last Updated : 18 Dec, 2019

Given a string and a substring, the task to find out the starting index for all the occurrences of a given substring in a string. Let’s discuss a few methods to solve the given task.

Method #1: Using Naive Method




# Python3 code to demonstrate
# to find all occurrences of substring in
# a string
  
# Initialising string
ini_string = 'xbzefdgstbzefzexezef'
  
# Initialising sub-string
sub_string = 'zef'
  
# Printing initial string and sub-string
print ("initial_strings : ", ini_string, "\nsubstring : ", sub_string)
  
res = []
flag = 0
k = 0
  
# Finding all occurrences of substring
# in a string using Naive method
for i in range(0, len(ini_string)):
    k = i
    flag = 0
    for j in range(0, len(sub_string)):
        if ini_string[k] != sub_string[j]:
            flag = 1
        if flag:
            break
        k = k + 1
    if flag == 0:
        res.append(i)
  
  
# printing result(
print ("resultant positions", str(res))
Output:
initial_strings :  xbzefdgstbzefzexezef 
substring :  zef
resultant positions [2, 10, 17]

&nsbp;
Method #2: Using list comprehension




# Python3 code to demonstrate
# to find all occurrences of substring in
# a string
  
# Initialising string
ini_string = 'xbzefdgstbzefzexezef'
  
# Initialising sub-string
sub_string = 'zef'
  
# Printing initial string and sub-string
print ("initial_strings : ", ini_string, "\nsubstring : ", sub_string)
  
res = []
# Finding all occurrences of substring
# in a string using list comprehension
res = [i for i in range(len(ini_string)) 
       if ini_string.startswith(sub_string, i)]
  
# printing result(
print ("resultant positions", str(res))
Output:



initial_strings :  xbzefdgstbzefzexezef 
substring :  zef
resultant positions [2, 10, 17]

 
Method #3: Using regex




# Python3 code to demonstrate
# to find all occurrences of substring in
# a string
import re
  
# Initialising string
ini_string = 'xbzefdgstbzefzexezef'
  
# Initialising sub-string
sub_string = 'zef'
  
# Printing initial string and sub-string
print ("initial_strings : ", ini_string, "\nsubstring : ", sub_string)
  
res = []
# Finding all occurrences of substring
# in a string using re.finditer
res = [m.start() for m in re.finditer(sub_string, ini_string)]
  
# printing result(
print ("resultant positions", str(res))
Output:
initial_strings :  xbzefdgstbzefzexezef 
substring :  zef
resultant positions [2, 10, 17]

 Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.  

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning – Basic Level Course




My Personal Notes arrow_drop_up
Recommended Articles
Page :