Interview Bite

Introduction

In Python, checking whether a string contains a specific substring is a common task. This functionality is frequently used in text processing, data validation, and other programming scenarios. In this guide, we will explore different methods to check if a string contains a substring in Python.

Methods to Check if a String Contains a Substring

1. Using the in Operator

The in operator is the simplest and most Pythonic way to check if a substring exists within a string.

# Example
text = "Python is amazing!"
substring = "amazing"

if substring in text:
    print("Substring found!")
else:
    print("Substring not found!")

Output:

Substring found!

2. Using the str.find() Method

The find() method returns the index of the first occurrence of the substring, or -1 if the substring is not found.

# Example
text = "Python is amazing!"
substring = "amazing"

if text.find(substring) != -1:
    print("Substring found!")
else:
    print("Substring not found!")

Output:

Substring found!

3. Using the str.index() Method

The index() method is similar to find(), but it raises a ValueError if the substring is not found.

# Example
text = "Python is amazing!"
substring = "amazing"

try:
    text.index(substring)
    print("Substring found!")
except ValueError:
    print("Substring not found!")

Output:

Substring found!

4. Using Regular Expressions

The re module provides advanced pattern-matching capabilities, which can be used to check for substrings.

import re

# Example
text = "Python is amazing!"
pattern = "amazing"

if re.search(pattern, text):
    print("Substring found!")
else:
    print("Substring not found!")

Output:

Substring found!

Interview Questions

• Question 1: How would you check if a string contains a substring without using the in operator?
• Question 2: What is the difference between find() and index() methods in Python?
• Question 3: How can you perform a case-insensitive substring search?
• Question 4: When would you use regular expressions instead of basic string methods?
• Question 5: Write a Python function to count the occurrences of a substring within a string.

Conclusion

Checking if a string contains a substring is an essential operation in Python programming. Depending on your requirements, you can use the in operator for simplicity, or leverage methods like find(), index(), or regular expressions for more advanced use cases. Mastering these techniques will help you handle text processing tasks efficiently.