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Python | Repeat and Multiply list extension

  • Last Updated : 27 Aug, 2019

Sometimes, while working with Python list, we can have a problem in which we need to extend a list in a very customized way. We may have to repeat contents of list and while doing that, each time new list must be a multiple of original list. This incremental expansion has applications in many domains. Let’s discuss a way in which this task can be performed.

Method : Using list comprehension
This task can be performed in a brute manner, but having a shorter implementation using list comprehension always is better. In this, we perform task in 2 steps, first we make a helper list to form a multiplication factor list and then cumulate the result using original list.

# Python3 code to demonstrate working of
# Repeat and Multiply list extension
# Using list comprehension
# initializing list
test_list = [4, 5, 6]
# printing original list
print("The original list is : " + str(test_list))
# Extension factor
N = 4
# Multiply factor 
M = 3
# Repeat and Multiply list extension
# Using list comprehension
temp = [1 * M**i for i in range(N)]
res = list([ele * tele for tele in temp for ele in test_list])
# printing result 
print("List after extension and multiplication : " + str(res))
Output :
The original list is : [4, 5, 6]
List after extension and multiplication : [4, 5, 6, 12, 15, 18, 36, 45, 54, 108, 135, 162]
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