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Python – Constant Multiplication over List
• Last Updated : 29 Dec, 2019

While working with the python lists, we can come over a situation in which we require to multiply constant to each element in the list. We possibly need to iterate and multiply constant to each element but that would increase the line of code. Let’s discuss certain shorthands to perform this task.

Method #1 : Using List Comprehension
List comprehension is just the short way to perform the task we perform using the naive method. This is mainly useful to save time and also is best among others when it comes to readability of the code.

 `# Python3 code to demonstrate  ` `# Constant Multiplication over List ` `# using list comprehension ` ` `  `# initializing list  ` `test_list ``=` `[``4``, ``5``, ``6``, ``3``, ``9``] ` ` `  `# printing original list ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# initializing K ` `K ``=` `4` ` `  `# using list comprehension ` `# Constant Multiplication over List ` `res ``=` `[x ``*` `K ``for` `x ``in` `test_list] ` ` `  `# printing result  ` `print` `(``"The list after constant multiplcation : "` `+` `str``(res)) `

Output :

```The original list is : [4, 5, 6, 3, 9]
The list after constant multiplcation : [16, 20, 24, 12, 36]
```

Method #2 : Using `map()` + operator.mul
This is similar to the above function but uses the operator.mul to multiply each element to other element from the other list of K formed before applying the map function. It multiplies the similar index elements of list.

 `# Python3 code to demonstrate  ` `# Constant Multiplication over List ` `# using map() + operator.mul ` `import` `operator ` ` `  `# initializing list  ` `test_list ``=` `[``4``, ``5``, ``6``, ``3``, ``9``] ` ` `  `# printing original list ` `print` `(``"The original list is : "` `+` `str``(test_list)) ` ` `  `# initializing K list ` `K_list ``=` `[``4``] ``*` `len``(test_list) ` ` `  `# using map() + operator.mul ` `# Constant Multiplication over List ` `res ``=` `list``(``map``(operator.mul, test_list, K_list)) ` ` `  `# printing result  ` `print` `(``"The list after constant multiplication : "` `+` `str``(res)) `

Output :

```The original list is : [4, 5, 6, 3, 9]
The list after constant multiplcation : [16, 20, 24, 12, 36]
```

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