Python | Add substring at specific index

In Python, String is immutable datatype, what this means is, that there are lot many restrictions when one handles its manipulation. The problem of adding something at a position at string is not possible, without the list reconstruction. Let’s discuss certain ways in which this task can be performed. 

Method #1 : Using list slicing This task can be performed using the list slicing. In this, we just slice the list into two parts, breaking at the target position and then rejoining it after inserting target substring at middle. 

Python3

# Python3 code to demonstrate
# Add substring at specific index
# using list slicing

# initializing string
test_string = 'geeksgeeks'

# initializing add_string
add_string = "for"

# printing original string
print("The original string : " + test_string)

# printing add string
print("The add string : " + add_string)

# initializing N
N = 5

# using list slicing
# Add substring at specific index
res = test_string[ : N] + add_string + test_string[N : ]

# print result
print("The string after performing addition : " + str(res))

Output : 

The original string : geeksgeeks
The add string : for
The string after performing addition : geeksforgeeks

Time complexity: O(1)
Auxiliary space: O(1)

Method #2 : Using join() + list() + insert() Another possible hack that can be performed in for the following problem is that converting the string to list and then adding the string at particular position and then performing the join. 

Python3

# Python3 code to demonstrate
# Add substring at specific index
# using join() + list() + insert()

# initializing string
test_string = 'geeksgeeks'

# initializing add_string
add_string = "for"

# printing original string
print("The original string : " + test_string)

# printing add string
print("The add string : " + add_string)

# initializing N
N = 5

# using join() + list() + insert()
# Add substring at specific index
res = list(test_string)
res.insert(N, add_string)
res = ''.join(res)

# print result
print("The string after performing addition : " + str(res))

Output : 

The original string : geeksgeeks
The add string : for
The string after performing addition : geeksforgeeks