Python Program to Replace all words except the given word

In this article, we will learn how to replace all words except the given word in a string in Python. This technique is useful for text processing where you want to mask certain words while preserving specific keywords.

Methods Used

The following are the various methods to accomplish this task:

• Using For Loop, split() & join() Functions

• Using List Comprehension

Problem Statement

Given an input string, we need to replace all words with a replacement character except for one specific word that should remain unchanged.

Input

inputString = 'hello tutorialspoint python codes'
inputWord = "tutorialspoint"
replaceChar = "@"

Expected Output

@ tutorialspoint @ @

In this example, all words are replaced with "@" symbol except "tutorialspoint" which remains unchanged.

Method 1: Using For Loop, split() and join() Functions

This method uses a traditional for loop approach with string manipulation functions:

• split() Splits a string into a list of words using whitespace as delimiter

• join() Joins elements of a list into a single string with specified separator

Example

# input string
inputString = 'hello tutorialspoint python codes'
print("Input String:", inputString)

# input word to preserve
inputWord = "tutorialspoint"

# replacement character
replaceChar = "@"

# split input string into list of words
wordsList = inputString.split(" ")

# traverse through each word
for index in range(len(wordsList)):
    element = wordsList[index]
    
    # replace word if it's not the input word
    if element != inputWord:
        wordsList[index] = replaceChar

# join the words back into a string
resultantString = " ".join(wordsList)

print("Replacing all words except input word with '@':")
print(resultantString)

Input String: hello tutorialspoint python codes
Replacing all words except input word with '@':
@ tutorialspoint @ @

Time Complexity: O(n) where n is the number of words

Space Complexity: O(n) for storing the word list

Method 2: Using List Comprehension

List comprehension provides a more concise and Pythonic way to achieve the same result in a single line.

Example

# input string
inputString = 'hello tutorialspoint python codes'
print("Input String:", inputString)

# input word to preserve
inputWord = "python"

# replacement character
replaceChar = "*"

# create new list using list comprehension
resultantList = [element if element == inputWord else replaceChar 
                for element in inputString.split()]

# join the list back to string
resultantString = " ".join(resultantList)

print("Replacing all words except input word with '*':")
print(resultantString)

Input String: hello tutorialspoint python codes
Replacing all words except input word with '*':
* * python *

Time Complexity: O(n) where n is the number of words

Space Complexity: O(n) for the result list

Comparison

Conclusion

Both methods effectively replace all words except a specified word in a string. Use list comprehension for concise code and for loops when you need more complex logic or better readability for beginners.