Python | Extract characters except of K string

Last Updated : 22 Apr, 2020

Sometimes, while working with Python strings, we can have a problem in which we require to extract all the elements of string except those which present in a substring. This is quite common problem and has application in many domains including those of day-day and competitive programming. Lets discuss certain ways in which this task can be performed.

Method #1 : Using loop
This is brute force approach to this problem. In this we employ not operator to test for element presence in master string and extract it if the element is not present in K string.

# Python3 code to demonstrate working of  
# Extract characters except of K string 
# Using loop 
  
# initializing strings 
test_str1 = "geeksforgeeks is best"
test_str2 = "fes"
  
# printing original strings 
print("The original string 1 is : " + test_str1) 
print("The original string 2 is : " + test_str2) 
  
# Extract characters except of K string 
# Using loop 
res = [] 
for ele in test_str1: 
    if ele not in test_str2: 
        res.append(ele) 
res = ''.join(res) 
  
# printing result  
print("String after removal of substring elements : " + str(res))  

Output :

The original string 1 is : geeksforgeeks is best
The original string 2 is : fes
String after removal of substring elements : gkorgk i bt

Method #2 : Using set operations
This task can also be performed by including set operations. One can perform a set difference to get difference of elements. The drawbacks are that order is not preserved and duplicates are removed.

# Python3 code to demonstrate working of  
# Extract characters except of K string 
# Using set operations 
  
# initializing strings 
test_str1 = "geeksforgeeks is best"
test_str2 = "fes"
  
# printing original strings 
print("The original string 1 is : " + test_str1) 
print("The original string 2 is : " + test_str2) 
  
# Extract characters except of K string 
# Using set operations 
res = ''.join(list(set(test_str1) - set(test_str2))) 
  
# printing result  
print("String after removal of substring elements : " + str(res))  

Output :

The original string 1 is : geeksforgeeks is best
The original string 2 is : fes
String after removal of substring elements : oti krbg

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