Python – Replace all numbers by K in given String

Given a string containing numbers, replace each number by K.

Input : test_str = ‘G4G is 4 all No. 1 Geeks’, K = ‘#’ 
Output : G#G is # all No. # Geeks 
Explanation : All numbers replaced by K. 

Input : test_str = ‘G4G is 4 all No. Geeks’, K = ‘#’ 
Output : G#G is # all No. Geeks 
Explanation : All numbers replaced by K.

Method #1 : Using replace() + isdigit()

In this, we check for numerics using isdigit() and replace() is used to perform the task of replacing the numbers by K.

Python3

# Python3 code to demonstrate working of
# Replace numbers by K in String
# Using replace() + isdigit()

# initializing string
test_str = 'G4G is 4 all No. 1 Geeks'

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

# initializing K
K = '@'

# loop for all characters
for ele in test_str:
    if ele.isdigit():
        test_str = test_str.replace(ele, K)

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

Output

The original string is : G4G is 4 all No. 1 Geeks
The resultant string : G@G is @ all No. @ Geeks

Method #2 : Using regex() + sub()

In this, appropriate regex is used to identify digits and sub() is used to perform replace.

Python3

# Python3 code to demonstrate working of
# Replace numbers by K in String
# Using regex() + sub()
import re

# initializing string
test_str = 'G4G is 4 all No. 1 Geeks'

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

# initializing K
K = '@'

# using regex expression to solve problem
res = re.sub(r'\d', K, test_str)

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

Output

The original string is : G4G is 4 all No. 1 Geeks
The resultant string : G@G is @ all No. @ Geeks

Method #3: Without using inbuilt functions

Python3

# Python3 code to demonstrate working of
# Replace numbers by K in String
# Using replace()

# initializing string
test_str = 'G4G is 4 all No. 1 Geeks'

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

# initializing K
K = '@'
digits="0123456789"

# loop for all characters
for ele in test_str:
    if ele in digits:
        test_str = test_str.replace(ele, K)

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

Output

The original string is : G4G is 4 all No. 1 Geeks
The resultant string : G@G is @ all No. @ Geeks

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)
Auxiliary Space: O(n)