Python check if string contains another string

String manipulation is a common task in any programming language. Python provides two common ways to check if a string contains another string.

Python check if string contains another string

Python string supports in operator. So we can use it to check if a string is part of another string or not. The in operator syntax is:

sub in str

It returns True if “sub” string is part of “str”, otherwise it returns False. Let’s look at some examples of using in operator in Python.

str1 = 'I love Python Programming'

str2 = 'Python'

str3 = 'Java'

print(f'"{str1}" contains "{str2}" = {str2 in str1}')
print(f'"{str1}" contains "{str2.lower()}" = {str2.lower() in str1}')
print(f'"{str1}" contains "{str3}" = {str3 in str1}')

if str2 in str1:
    print(f'"{str1}" contains "{str2}"')
else:
    print(f'"{str1}" does not contain "{str2}"')

Output:

"I love Python Programming" contains "Python" = True
"I love Python Programming" contains "python" = False
"I love Python Programming" contains "Java" = False
"I love Python Programming" contains "Python"

If you are not familiar with f-prefixed strings in Python, it’s a new way for string formatting introduced in Python 3.6. You can read more about it at f-strings in Python.

When we use in operator, internally it calls __contains__() function. We can use this function directly too, however it’s recommended to use in operator for readability purposes.

s = 'abc'

print('s contains a =', s.__contains__('a'))
print('s contains A =', s.__contains__('A'))
print('s contains X =', s.__contains__('X'))

Output:

s contains a = True
s contains A = False
s contains X = False

Using find() to check if a string contains another substring

We can also use string find() function to check if string contains a substring or not. This function returns the first index position where substring is found, else returns -1.

str1 = 'I love Python Programming'

str2 = 'Python'

str3 = 'Java'

index = str1.find(str2)
if index != -1:
    print(f'"{str1}" contains "{str2}"')
else:
    print(f'"{str1}" does not contain "{str2}"')

index = str1.find(str3)
if index != -1:
    print(f'"{str1}" contains "{str3}"')
else:
    print(f'"{str1}" does not contain "{str3}"')

Output:

"I love Python Programming" contains "Python"
"I love Python Programming" does not contain "Java"

You can checkout complete python script and more Python examples from our GitHub Repository.