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# Python – Incremental List Extension

• Last Updated : 27 Dec, 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 add a number to 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 addition factor list and then cumulate the result using original list.

 `# Python3 code to demonstrate working of``# Incremental List Extension``# Using list comprehension`` ` `# initializing list``test_list ``=` `[``7``, ``8``, ``9``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Extension factor``N ``=` `4`` ` `# Addition factor ``M ``=` `3`` ` `# Incremental List Extension``# Using list comprehension``temp ``=` `[``1` `*` `M``*``*``i ``for` `i ``in` `range``(N)]``temp[``0``] ``=` `0``res ``=` `list``([ele ``+` `tele ``for` `tele ``in` `temp ``for` `ele ``in` `test_list])`` ` `# printing result ``print``(``"List after extension and addition : "` `+` `str``(res))`
Output :
```The original list is : [7, 8, 9]
List after extension and addition : [7, 8, 9, 10, 11, 12, 16, 17, 18, 34, 35, 36]
```

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