# Python – K Summation from Two lists

• Last Updated : 06 Mar, 2020

Sometimes, while working with Python lists we can have a problem in which we need to find summation of lists taking elements from two different lists. This kind of application can come in different domains such as web development. Lets discuss certain ways in which this task can be performed.

Method #1 : Using loop
This task can be done using loop in a brute force manner. We run a nested loop one for each list and when we find a match we update the result list with the pair.

 `# Python3 code to demonstrate ``# K Summation from Two lists``# using loop`` ` `# Initializing lists``test_list1 ``=` `[``3``, ``2``, ``5``]``test_list2 ``=` `[``4``, ``3``, ``6``, ``8``, ``7``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Initializing K ``K ``=` `9`` ` `# K Summation from Two lists``# using loop``res ``=` `[]``for` `idx ``in` `test_list1:``    ``val_req ``=` `K ``-` `idx``    ``for` `j ``in` `test_list2:``        ``if` `j ``=``=` `val_req:``            ``x, y ``=` `j, idx``            ``res.append((x, y))`` ` `# printing result ``print` `(``"Summation pairs among lists : "` `+` `str``(res))`

Output :

```The original list 1 is : [3, 2, 5]
The original list 2 is : [4, 3, 6, 8, 7]
Summation pairs among lists : [(6, 3), (7, 2), (4, 5)]
```

Method #2 : Using list comprehension
This is yet another way in which this task can be performed. In this, we perform similar task as above. The difference is that this is one liner and we perform task in one line.

 `# Python3 code to demonstrate ``# K Summation from Two lists``# using list comprehension`` ` `# Initializing lists``test_list1 ``=` `[``3``, ``2``, ``5``]``test_list2 ``=` `[``4``, ``3``, ``6``, ``8``, ``7``]`` ` `# printing original lists``print``(``"The original list 1 is : "` `+` `str``(test_list1))``print``(``"The original list 2 is : "` `+` `str``(test_list2))`` ` `# Initializing K ``K ``=` `9`` ` `# K Summation from Two lists``# using list comprehension``res ``=` `[(a, b) ``for` `a ``in` `test_list1 ``for` `b ``in` `test_list2 ``if` `a ``+` `b ``=``=` `K]`` ` `# printing result ``print` `(``"Summation pairs among lists : "` `+` `str``(res))`

Output :

```The original list 1 is : [3, 2, 5]
The original list 2 is : [4, 3, 6, 8, 7]
Summation pairs among lists : [(6, 3), (7, 2), (4, 5)]
```

My Personal Notes arrow_drop_up