Python – Check if String Contains Substring

In this tutorial, we are going to see different ways to check if a string contains substring and if it does, look for its index. Also, we will check the existence of a substring ignoring the case.
 

Check if String Contains Substring Using ‘IN’ operator

The “in” operator in Python can be used to check if a given string exists in another string. For example:

str = "Welcome to StackHowTo."
# Check if String Contains Substring
if "StackHowTo" in str:
    print ('Substring found')
else:
    print('Substring not found')

Output:

Substring found

Check if String Contains Substring Using ‘NOT IN’ operator

We can also use the ‘NOT IN’ operator to check the opposite scenario. For example:

str = "Welcome to StackHowTo."
# Check if String Contains Substring
if "StackHowTo" not in str:
    print('Substring not found')
else:
    print ('Substring found')

Output:

Substring found

Check if String Contains Substring in a Case-insensitive Way

To check whether a given string contains a substring in a case-insensitive way, i.e. ignoring case, we must first transform both strings to lowercase, and then use the “in” or “not in” operator to check if substring exist. For example:

str = "Welcome to StackHowTo."
# Convert both strings to lowercase
if "STACKHOWTO".lower() in str.lower():
    print ('Substring found')
else:
    print('Substring not found')

Output:

Substring found

Check if String Contains Substring Using Regex

We can also use python’s regex “re” module to check if a given string exists within another string. For example:

import re

str = "Welcome to StackHowTo."
# Create a pattern to match the string 'StackHowTo
motif = re.compile("StackHowTo")
# searches for the pattern in the string and returns the corresponding object
obj = motif.search(str)
# check if the object is not Null
if obj:
    print ('Substring found')
else:
    print('Substring not found')

Output:

Substring found