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About Yatin

Working as a Technical Lead in the Information Technology sector where I'm primarily involved with projects based on Java/J2EE Technologies platform (such as Spring, Spring Boot, Hibernate, Redis, etc.), novel UI technologies (Angular & React), Docker, and AWS. Recently completed the AWS Solution Architect Associate Certification.

Python String contains() method Tutorial

Hello in this tutorial, we will understand Python String contains() method.

1. Introduction

The contains in python is used to check whether a string contains a substring or not. A substring is the sequence of characters within a string. We will explore the below methods to check if a string contains another string or not.

  • The find() method checks if a substring is part of the string or not. If the string contains the given substring the method returns the starting index of the substring else it will return -1. It is represented by the following syntax i.e. string.find(substring)
  • The index() method checks if a substring is part of the string or not. If found it returns the starting index of the first occurrence of a substring and if not it generates a ValueError exception which can be handled with the help of the try-expect-else block in python. It is represented by the following syntax i.e. string.index(substring)
  • The count() method checks the occurrence of a substring in the string. If found it returns 1 otherwise 0. It is represented by the following syntax i.e. string.count(substring)
  • The replace() method is used to replace the occurrences of a substring with a new string. It is represented by the following syntax i.e. string.replace(old_word, new_word, no_of_occurences) where no_of_occurences is an optional field that denotes the number of times you want to replace the old substring with the new substring
  • The in operator checks if the substring is a part of the string or not. If present it returns true otherwise false. It is represented by the following syntax i.e. substring in string
  • Using the regular expression to check if the substring is a part of the string or not through the pattern matching. For this, we will use a python in-built module known as re. This module contains a method known as search which you can use to match a substring pattern
  • We will use also use another python in-built module known as operator. This module contains a method known as contains() which you can use to check the presence of a substring in a string

Let us see these different ways in action.

1.1 Setting up Python

If someone needs to go through the Python installation on Windows, please watch this link. You can download the Python from this link.

2. Python String contains() Tutorial

I am using JetBrains PyCharm as my preferred IDE. You are free to choose the IDE of your choice.

2.1 Python String contains() Tutorial

Let us understand the different ways through programming.

Python String contains()

# python string contain() method tutorial
# import statement
import operator
# import statement
from re import search
# approach 1 - index()
def index(string, search_key):
    try:
        string.index(search_key)
        print('Found.')
    except ValueError:
        print('Search key not found.')
# approach 2 - find()
def find(string, search_key):
    if string.find(search_key) != -1:
        print('Found.')
    else:
        print('Search key not found.')
# approach 3 - count()
def count(string, search_key_1, search_key_2):
    x = string.count(search_key_1)
    print('Is search key 1 = {} present in the given string = {}'.format(search_key_1, x))
    y = string.count(search_key_2)
    print('Is search key 2 = {} present in the given string = {}'.format(search_key_2, y))
# approach 4 - replace()
def replace(string, old_word, new_word, no_of_occurrences):
    z = string.replace(old_word, new_word, no_of_occurrences)
    print('Replaced string = {}'.format(z))
# approach 5 - in operator
def in_operator(string, search_key):
    if search_key in string:
        print('Found.')
    else:
        print('Search key not found.')
# approach 6 - regex expression
def regex(string, search_key):
    if search(search_key, string):
        print('Found.')
    else:
        print('Search key not found.')
# approach 7 - using operator module
def operator_mod(string, search_key):
    if operator.contains(string, search_key):
        print('Found.')
    else:
        print('Search key not found.')
# main() method
def main():
    string = 'What am I even tripping for? Everything’s gonna work out exactly the way it’s supposed to'
    print('\n--- Approach 1 ---\n')
    index(string, 'tripping')
    print('\n--- Approach 2 ---\n')
    find(string, 'supposed')
    print('\n--- Approach 3 ---\n')
    count(string, 'tripping', 'done')
    print('\n--- Approach 4 ---\n')
    no_of_occurrences = 1
    replace(string, 'tripping', 'TRIPPING', no_of_occurrences)
    print('\n--- Approach 5 ---\n')
    in_operator(string, 'going')
    print('\n--- Approach 6 ---\n')
    regex(string, 'geek')
    print('\n--- Approach 7 ---\n')
    operator_mod(string, 'gonna')
# driver code
if __name__ == '__main__':
    main()

If everything goes well the following output will be shown in the IDE console.

Console Output

--- Approach 1 ---
Found.
--- Approach 2 ---
Found.
--- Approach 3 ---
Is search key 1 = tripping present in the given string = 1
Is search key 2 = done present in the given string = 0
--- Approach 4 ---
Replaced string = What am I even TRIPPING for? Everything’s gonna work out exactly the way it’s supposed to
--- Approach 5 ---
Search key not found.
--- Approach 6 ---
Search key not found.
--- Approach 7 ---
Found.

That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share!

3. Summary

In this tutorial, we learned:

  • contains() method in python programming to find the presence of a substring in a string
  • Sample program to understand the different use cases

You can download the source code of this tutorial from the Downloads section.

4. Download the Project

This was a python programming tutorial to understand the different use cases for finding the presence of a substring in a string.

Download
You can download the full source code of this example here: Python String contains() method Tutorial

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