Python – Specific Range Addition in List

Sometimes, while working with Python, we need to perform an edition in the Python list. And sometimes we need to perform this to a specific index range in it. This kind of application can have applications in many domains. Let us discuss certain ways in which this task can be performed. 

Method #1: Using loop

This is a brute way in which this task can be performed. In this, we just iterate through the specified range in which the edition has to be performed.

Python3

# Python3 code to demonstrate
# Specific Range Addition in List
# using loop

# Initializing list
test_list = [4, 5, 6, 8, 10, 11]

# printing original list
print("The original list is : " + str(test_list))

# Initializing range
i, j = 2, 5

# Specific Range Addition in List
# using loop
for idx in range(i, j):
    test_list[idx] += 3

# printing result
print("List after range addition : " + str(test_list))

Output : 

The original list is : [4, 5, 6, 8, 10, 11]
List after range addition : [4, 5, 9, 11, 13, 11]

Time Complexity: O(n) where n is the number of elements in the list “test_list”.  
Auxiliary Space: O(1), constant extra space is needed

Method #2: Using list comprehension

This task can also be performed using list comprehension. This method uses the same way as above but it’s a shorthand for the above. 

Python3

# Python3 code to demonstrate
# Specific Range Addition in List
# using list comprehension

# Initializing list
test_list = [4, 5, 6, 8, 10, 11]

# printing original list
print("The original list is : " + str(test_list))

# Initializing range
i, j = 2, 5

# Specific Range Addition in List
# using list comprehension
test_list[i: j] = [ele + 3 for ele in test_list[i: j]]

# printing result
print("List after range addition : " + str(test_list))

Output : 

The original list is : [4, 5, 6, 8, 10, 11]
List after range addition : [4, 5, 9, 11, 13, 11]

Method #3: Using numpy Here is one approach using numpy library:

Note: Install numpy module using command “pip install numpy”

Python3

# Importing numpy library
import numpy as np

# Initializing list
test_list = [4, 5, 6, 8, 10, 11]

# printing original list
print("The original list is : " + str(test_list))

# Initializing range
i, j = 2, 5

# Specific Range Addition in List using numpy
test_list = np.array(test_list)
test_list[i:j] += 3

# printing result
print("List after range addition : " + str(test_list.tolist()))
# This code is contributed by Edula Vinay Kumar Reddy

Output:

The original list is : [4, 5, 6, 8, 10, 11]
List after range addition : [4, 5, 9, 11, 13, 11]

Time Complexity: O(n), where n is the length of the list.
Auxiliary Space: O(n), as a numpy array of the same length as the list is created.

Explanation:

• Import the numpy library
• Convert the list to a numpy array
• Add 3 to the specific range (i:j) of the numpy array
• Convert the numpy array back to a list and print the result.

Method 4: Using the slice notation and the built-in map function.

Python3

# Initializing list
test_list = [4, 5, 6, 8, 10, 11]

# Initializing range(custom)
i, j = 2, 5

# Specific Range Addition in List using map and slice
test_list[i:j] = map(lambda x: x + 3, test_list[i:j])

# printing result
print("List after range addition : " + str(test_list))

Output

List after range addition : [4, 5, 9, 11, 13, 11]

Time complexity of O(n), where n is the length of the list. 
Auxiliary space: O(1), as we’re only modifying the original list and not creating any additional data structures.