How to Check if a String contains a Substring in Python?

By / August 6, 2022

A substring is a sequence of characters within a String. The following are the methods in Python to check if a string contains another string i.e. substring.

  1. By using find() method
  2. By using in operator
  3. By using count() method
  4. By using str.index() method
  5. By using operator.contains() method

Method 1: By using find() method

The method find() checks whether a string contains a particular substring or not. If the string contains that particular substring, the method returns the starting index of the substring else it returns -1.

Syntax: string.find(substring)

Example: Checking for the presence of substring within the string using find() method

str="Safa Mulani is a student of Engineering discipline." 
sub1="Safa" 
sub2="Engineering" 

print(str.find(substring1)) 

print(str.find(substring2))

Output:

0
28

Method 2: By using in operator

The in operator checks for the presence of substring within a string, if the substring is present it returns TRUE else it returns FALSE.

Syntax: substring in string_object

Example: Checking for the presence of substring within the string using in operator

str="Safa Mulani is a student of Engineering discipline." 
sub1="Safa" 
sub2="Done" 

print(sub1 in str) 

print(sub2 in str)

Output:

True
False

Method 3: By using count() method

The count() method checks for the occurrence of substring in a string. If the substring is not found in the string, it returns 0.

Syntax: string.count(substring)

Example: Checking for the presence of substring within a string using count() method

str="Safa Mulani is a student of Engineering discipline." 
sub1="Safa" 
sub2="student" 
sub3="Done"
print(str.count(sub1)) 

print(str.count(sub2))

print(str.count(sub3))

Output:

1
1
0

Method 4: By using index() method

The method checks for the presence of a substring in a string. If the substring is not present in the string then it doesn’t return any value, rather it generates a ValueError.

Syntax: string.index(substring)

Example: Checking for the presence of a substring in a string using the index() method

str = "Safa is a Student."
try :  
    result = str.index("Safa") 
    print ("Safa is present in the string.") 
except : 
    print ("Safa is not present in the string.")

Output:

Safa is present in the string.

Method 5: By using the operator.contains() method

Syntax: operator.contains(string,substring)

Example: Checking for the presence of a substring in the string using the operator.contains() method

import operator 
  
str = "Safa is a Student."
  
if operator.contains(str, "Student"): 
    print ("Student is present in the string.") 
else : 
    print ("Student is not present in the string.")

Output: Student is present in the string.

References

  • Python String