Python | Check if substring present in string

Lets solve this general problem of finding if a particular piece of string is present in a larger string in different ways. This is a very common kind of problem every programmer comes across aleast once in his/her lifetime. This article gives various techniques to solve it.

Method 1 : Using in operator
The in operator is the most generic, fastest method to check for a substring, the power of in operator in python is very well known and is used in many operations across the entire language.

# Python 3 code to demonstrate  
# checking substring in string 
# using in operator 
  
# initializing string  
test_str = "GeeksforGeeks"
  
# using in to test 
# for substring 
print ("Does for exists in GeeksforGeeks ? : ") 
if "for" in test_str : 
    print ("Yes, String found") 
else :  
    print ("No, String not found") 

Output :

Does for exists in GeeksforGeeks ? : 
Yes, String found

Method 2 : Using str.find()
str.find() method is generally used to get the lowest index at which the string occurs, but also returns -1, if string is not present, hence if any value returns >= 0, string is present, else not present.

# Python 3 code to demonstrate  
# checking substring in string 
# using str.find() 
  
# initializing string  
test_str = "GeeksforGeeks"
  
# using str.find() to test 
# for substring 
res = test_str.find("for") 
if res >= 0: 
    print ("for is present in GeeksforGeeks") 
else : 
    print ("for is not present in GeeksforGeeks") 

Output :

for is present in GeeksforGeeks

Method 3 : Using str.index()
This method can be used to performs the similar task, but like str.find(), it doesn’t return a value, but a ValueError if string is not present, hence catching the exception is the way to check for string in substring.

# Python 3 code to demonstrate  
# checking substring in string 
# using str.index() 
  
# initializing string  
test_str = "GeeksforGeeks"
  
# using str.index() to test 
# for substring 
try :  
    res = test_str.index("forg") 
    print ("forg exists in GeeksforGeeks") 
except : 
    print ("forg does not exists in GeeksforGeeks") 

Output :

forg does not exists in GeeksforGeeks

Method 4 : Using operator.contains()
This is lesser known method to check for substring in a string, this method is also effective in accomplishing this task of checking a string in a string.

# Python 3 code to demonstrate  
# checking substring in string 
# using operator.contains() 
import operator 
  
# initializing string  
test_str = "GeeksforGeeks"
  
# using operator.contains() to test 
# for substring 
if operator.contains(test_str, "for"): 
    print ("for is present in GeeksforGeeks") 
else : 
    print ("for is not present in GeeksforGeeks") 

Output :

for is present in GeeksforGeeks

My Personal Notes

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