Python Program to repeat elements at custom indices

Given a List, the following program repeats those elements which are at a custom index, these custom indices are provided to it as a separate list.

Input : test_list = [4, 6, 7, 3, 1, 9, 2, 19], idx_list = [3, 1, 6] 
Output : [4, 6, 6, 7, 3, 3, 1, 9, 2, 2, 19] 
Explanation : All required index elements repeated, Eg. 6 repeated as it is at index 1.
Input : test_list = [4, 6, 7, 3, 1, 9, 2, 19], idx_list = [1, 6] 
Output : [4, 6, 6, 7, 3, 1, 9, 2, 2, 19] 
Explanation : All required index elements repeated, 6 repeated as it is at index 1. 

Method : Using loop and extend()

In this, we perform the task of repeating each element in case it is the required index to be repeated using extend() and loop is used to iterate for every index. The enumerate() is used to get all the indices along with elements.

Program:

Python3

# initializing list
test_list = [4, 6, 7, 3, 1, 9, 2, 19]

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

# initializing index list
idx_list = [3, 1, 4, 6]

res = []
for idx, ele in enumerate(test_list):
    if idx in idx_list:

        # incase of repetition
        res.extend([ele, ele])
    else :
        res.append(ele)

# printing result
print("The Custom elements repetition : " + str(res))

Output:

The original list is : [4, 6, 7, 3, 1, 9, 2, 19]

The Custom elements repetition : [4, 6, 6, 7, 3, 3, 1, 1, 9, 2, 2, 19]

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