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Python | Pair summation of list elements
• Last Updated : 03 Oct, 2019

Sometimes, while working with Python list, one can have a problem in which one needs to find perform the summation of list in pair form. This is useful as a subproblem solution of bigger problem in web development and day-day programming. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using loop
This is the brute force method to perform this particular task. In this, we just iterate the list till last element in skipped manner to get all the pair sums in other list in an iterative way.

 `# Python3 code to demonstrate working of``# Pair summation of list``# Using loop`` ` `# initializing list``test_list ``=` `[``4``, ``5``, ``8``, ``9``, ``10``, ``17``]`` ` `# printing list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# Pair summation of list``# Using loop``res ``=` `[]``for` `ele ``in` `range``(``0``, ``len``(test_list), ``2``):``    ``res.append(test_list[ele] ``+` `test_list[ele ``+` `1``])`` ` `# Printing result``print``(``"Pair summation of list : "` `+` `str``(res))`
Output :
```
The original list : [4, 5, 8, 9, 10, 17]
Pair summation of list : [9, 17, 27]
```

Method #2 : Using `zip()` + list comprehension
This task can also be performed using the combination of above functionalities. In this, we just iterate the list and the task of combining pairs is performed by zip(). Works only on Python2.

 `# Python code to demonstrate working of``# Pair summation of list``# zip() + list comprehension`` ` `# initializing list``test_list ``=` `[``4``, ``5``, ``8``, ``9``, ``10``, ``17``]`` ` `# printing list``print``(``"The original list : "` `+` `str``(test_list))`` ` `# Pair summation of list``# zip() + list comprehension``res ``=` `[i ``+` `j ``for` `i, j ``in` `zip``(test_list, test_list[``1``:])[::``2``]]`` ` `# Printing result``print``(``"Pair summation of list : "` `+` `str``(res))`
Output :
```
The original list : [4, 5, 8, 9, 10, 17]
Pair summation of list : [9, 17, 27]
```

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