Python – Replace all words except the given word

Given a string. The task is to replace all the words with ‘?’ except the given word K.

Examples:

Input : test_str = ‘gfg is best for geeks’, K = “gfg”, repl_char = “?” 
Output : gfg ? ? ? ? 
Explanation : All words except gfg is replaced by ?.

Input : test_str = ‘gfg is best for gfg’, K = “gfg”, repl_char = “?” 
Output : gfg ? ? ? gfg 
Explanation : All words except gfg is replaced by ?. 

Method #1 : Using split() + join() + loop

This is a brute way in which this task can be performed. In this, we perform the task of changing the string to word list using split() and then check for K word, if not found, replace it by the appropriate value. And at last, convert back to the string using join().

Python3

# Python3 code to demonstrate working of
# Replace all words not K
# Using join() + split() + loop

# initializing string
test_str = 'gfg is best for geeks gfg is for cs I love gfg'

# printing original string
print("The original string is : " + str(test_str))

# initializing K
K = "gfg"

# initializing repl_char
repl_char = "?"

# extracting words
temp = test_str.split(" ")
for idx in range(len(temp)):
    ele = temp[idx]

    # replace non K with repl_char
    if not ele == K:
        temp[idx] = repl_char

# joining result
res = " ".join(temp)

# printing result
print("The resultant string : " + str(res))

Output:

The original string is : gfg is best for geeks gfg is for cs I love gfg The resultant string : gfg ? ? ? ? gfg ? ? ? ? ? gfg

Time Complexity: O(n)

Auxiliary Space: O(n)

Method #2: Using list comprehension

This is yet another way in which this task can be performed. In this, we iterate for elements and perform the task using one-liner using similar functionality as the above method.

Python3

# Python3 code to demonstrate working of
# Replace all words not K
# Using list comprehension

# initializing string
test_str = 'gfg is best for geeks gfg is for cs I love gfg'

# printing original string
print("The original string is : " + str(test_str))

# initializing K
K = "gfg"

# initializing repl_char
repl_char = "?"

# using one-liner to solve this problem
res = " ".join(
    [repl_char if not ele == K else ele for ele in test_str.split()])

# printing result
print("The resultant string : " + str(res))

Output:

The original string is : gfg is best for geeks gfg is for cs I love gfg The resultant string : gfg ? ? ? ? gfg ? ? ? ? ? gfg

Time Complexity: O(n)

Auxiliary Space: O(n)