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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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