# Python | Repeat and Multiply list extension

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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