# Python – Replace index elements with elements in Other List

• Difficulty Level : Medium
• Last Updated : 06 Mar, 2020

Sometimes, while working with Python data, we can have a problem in which we have two lists and we need to replace positions in one list with the actual elements from other list. Lets discuss certain ways in which this task can be performed.

Method #1 : Using list comprehension
This is one way to solve this problem. In this we just iterate through the list and assign the index value from one list to other.

 `# Python3 code to demonstrate ``# Replace index elements with elements in Other List``# using list comprehension`` ` `# Initializing lists``test_list1 ``=` `[``'Gfg'``, ``'is'``, ``'best'``]``test_list2 ``=` `[``0``, ``1``, ``2``, ``1``, ``0``, ``0``, ``0``, ``2``, ``1``, ``1``, ``2``, ``0``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Replace index elements with elements in Other List``# using list comprehension``res ``=` `[test_list1[idx] ``for` `idx ``in` `test_list2]``             ` `# printing result ``print` `(``"The lists after index elements replacements is : "` `+` `str``(res))`

Output :

The original list 1 is : [‘Gfg’, ‘is’, ‘best’]
The original list 2 is : [0, 1, 2, 1, 0, 0, 0, 2, 1, 1, 2, 0]
The lists after index elements replacements is : [‘Gfg’, ‘is’, ‘best’, ‘is’, ‘Gfg’, ‘Gfg’, ‘Gfg’, ‘best’, ‘is’, ‘is’, ‘best’, ‘Gfg’]

Method #2 : Using `map()` + lambda
The combination of above functions can be used to perform this task. In this, we perform task of extension of logic to every element using map() and lambda functions.

 `# Python3 code to demonstrate ``# Replace index elements with elements in Other List``# using map() + lambda`` ` `# Initializing lists``test_list1 ``=` `[``'Gfg'``, ``'is'``, ``'best'``]``test_list2 ``=` `[``0``, ``1``, ``2``, ``1``, ``0``, ``0``, ``0``, ``2``, ``1``, ``1``, ``2``, ``0``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Replace index elements with elements in Other List``# using map() + lambda``res ``=` `list``(``map``(``lambda` `idx: test_list1[idx], test_list2))``             ` `# printing result ``print` `(``"The lists after index elements replacements is : "` `+` `str``(res))`

Output :

The original list 1 is : [‘Gfg’, ‘is’, ‘best’]
The original list 2 is : [0, 1, 2, 1, 0, 0, 0, 2, 1, 1, 2, 0]
The lists after index elements replacements is : [‘Gfg’, ‘is’, ‘best’, ‘is’, ‘Gfg’, ‘Gfg’, ‘Gfg’, ‘best’, ‘is’, ‘is’, ‘best’, ‘Gfg’]

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