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Python – Negative index of Element in List
• Last Updated : 20 Oct, 2020

Given a list of elements, find its negative index in the List.

Input : test_list = [5, 7, 8, 2, 3, 5, 1], K = 2
Output : -4
Explanation : 2 is 4th element from rear.

Input : test_list = [5, 7, 8, 2, 3, 5, 1], K = 5
Output : -2
Explanation : 5 is 2nd element from rear.

Method #1 : Using index() + len()

In this, we get the index of the element using index(), and then subtract it from the list length to get the required result.

## Python3

 `# Python3 code to demonstrate working of``# Negative index of Element``# Using index() + len()` `# initializing list``test_list ``=` `[``5``, ``7``, ``8``, ``2``, ``3``, ``5``, ``1``]` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))` `# initializing Element``K ``=` `3` `# getting length using len() and subtracting index from it``res ``=` `len``(test_list) ``-` `test_list.index(K)` `# printing result``print``(``"The required Negative index : -"` `+` `str``(res))`

Output:

```The original list is : [5, 7, 8, 2, 3, 5, 1]
The required Negative index : -3```

Method #2 : Using ~ operator + list slicing + index()

In this, we reverse the list using slicing, and use ~ operator to get negation, index() is used to get the desired negative index.

## Python3

 `# Python3 code to demonstrate working of``# Negative index of Element``# Using ~ operator + list slicing + index()` `# initializing list``test_list ``=` `[``5``, ``7``, ``8``, ``2``, ``3``, ``5``, ``1``]` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))` `# initializing Element``K ``=` `3` `# -1 operator to reverse list, index() used to get index``res ``=` `~test_list[::``-``1``].index(K)` `# printing result``print``(``"The required Negative index : "` `+` `str``(res))`

Output:

```The original list is : [5, 7, 8, 2, 3, 5, 1]
The required Negative index : -3```

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