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Python | Element indices Summation

• Last Updated : 19 Feb, 2020

Usually, we require to find the sum of index, in which the particular value is located. There are many method to achieve that, using index() etc. But sometimes require to find all the indices of a particular value in case it has multiple occurrences in list. Lets discuss certain ways to do so.

Method #1 : Naive Method + sum()
We can achieve this task by iterating through the list and check for that value and just append the value index in new list and print that. This is the basic brute force method to achieve this task. The sum() is used to perform sum of list.

 `# Python code to demonstrate ``# Element indices Summation``# using naive method + sum()`` ` `# initializing list ``test_list ``=` `[``1``, ``3``, ``4``, ``3``, ``6``, ``7``]`` ` `# printing initial list ``print` `(``"Original list : "` `+` `str``(test_list))`` ` `# using naive method``# Element indices Summation``# to find indices for 3``res_list ``=` `[]``for` `i ``in` `range``(``0``, ``len``(test_list)) :``    ``if` `test_list[i] ``=``=` `3` `:``        ``res_list.append(i)``res ``=` `sum``(res_list)`` ` `# printing resultant list ``print` `(``"New indices summation : "` `+` `str``(res))`
Output :
```Original list : [1, 3, 4, 3, 6, 7]
New indices summation : 4
```

Method #2 : Using list comprehension + `sum()`
List comprehension is just the shorthand technique to achieve the brute force task, just uses lesser lines of codes to achieve the task and hence saves programmers time. The sum() is used to perform sum of list.

 `# Python code to demonstrate ``# Element indices Summation``# using list comprehension + sum()`` ` `# initializing list ``test_list ``=` `[``1``, ``3``, ``4``, ``3``, ``6``, ``7``]`` ` `# printing initial list ``print` `(``"Original list : "` `+` `str``(test_list))`` ` `# using list comprehension + sum()``# Element indices Summation``# to find indices for 3``res_list ``=` `[i ``for` `i ``in` `range``(``len``(test_list)) ``if` `test_list[i] ``=``=` `3``]``res ``=` `sum``(res_list)`` ` `# printing resultant list ``print` `(``"New indices summation : "` `+` `str``(res))`
Output :
```Original list : [1, 3, 4, 3, 6, 7]
New indices summation : 4
```

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