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Python | Check if a Substring is Present in a Given String

  • Difficulty Level : Easy
  • Last Updated : 18 May, 2020

Given two strings, check if s1 is there in s2.

Examples:

Input : s1 = geeks s2=geeks for geeks
Output : yes

Input : s1 = geek s2=geeks for geeks
Output : yes

We can iteratively check for every word, but Python provides us an inbuilt function find() which checks if a substring is present in the string, which is done in one line.
find() function returns -1 if it is not found, else it returns the first occurrence, so using this function this problem can be solved.
Method 1: Using user defined function.




# function to check if small string is 
# there in big string
def check(string, sub_str):
    if (string.find(sub_str) == -1):
        print("NO")
    else:
        print("YES")
            
# driver code
string = "geeks for geeks"
sub_str ="geek"
check(string, sub_str)

Output:



YES          

Method 2: Using “count()” method:-




def check(s2, s1): 
    if (s2.count(s1)>0):     
        print("YES"
    else
        print("NO"
              
s2 = "A geek in need is a geek indeed"
s1 ="geek"
check(s2, s1) 

Output:

YES          

Method 3: Using regular expressions
RegEx can be used to check if a string contains the specified search pattern. Python has a built-in package called re, which can be used to work with Regular Expressions.




# When you have imported the re module, you can start using regular expressions.
import re
  
# Take input from users
MyString1 =  "A geek in need is a geek indeed"
MyString2 ="geek"
  
# re.search() returns a Match object if there is a match anywhere in the string
if re.search( MyString2, MyString1 ):
    print("YES,string '{0}' is present in string '{1}' " .format(MyString2,MyString1))
else:
    print("NO,string '{0}' is not present in string {1} " .format(MyString2, MyString1) )

Output:

YES,string 'geek' is present in string 'A geek in need is a geek indeed' 

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