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# Python – Extract element from list succeeded by K

• Last Updated : 11 Oct, 2020

Given a list, extract the elements which are having K as the next element.

Input : test_list = [2, 3, 5, 7, 8, 5, 3, 5], K = 3
Output : [2, 5]
Explanation : Elements before 3 are 2, 5.

Input : test_list = [2, 3, 5, 7, 8, 5, 3, 8], K = 8
Output : [7, 3]
Explanation : Elements before 8 are 7, 3.

Method #1: Using loop

In this, we iterate the list and look for each K, and extract the element preceding it.

## Python3

 `# Python3 code to demonstrate working of``# Extract elements succeeded by K``# Using loop`` ` `# initializing list``test_list ``=` `[``2``, ``3``, ``5``, ``7``, ``8``, ``5``, ``3``, ``5``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# initializing K``K ``=` `5`` ` `# Using loop to extract elements succeeded by K``res ``=` `[]``for` `idx ``in` `range``(``len``(test_list) ``-` `1``):`` ` `    ``# checking for succession``    ``if` `test_list[idx ``+` `1``] ``=``=` `K:``        ``res.append(test_list[idx])`` ` `# printing result``print``(``"Extracted elements list : "` `+` `str``(res))`

Output

```The original list is : [2, 3, 5, 7, 8, 5, 3, 5]
Extracted elements list : [3, 8, 3]
```

Method #2: Using list comprehension

Another way to solve this question, in this, we use list comprehension as shorthand to solve the problem of getting elements.

## Python3

 `# Python3 code to demonstrate working of``# Extract elements succeeded by K``# Using list comprehension`` ` `# initializing list``test_list ``=` `[``2``, ``3``, ``5``, ``7``, ``8``, ``5``, ``3``, ``5``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# initializing K``K ``=` `5`` ` `# List comprehension used as shorthand``res ``=` `[test_list[idx]``       ``for` `idx ``in` `range``(``len``(test_list) ``-` `1``) ``if` `test_list[idx ``+` `1``] ``=``=` `K]`` ` `# printing result``print``(``"Extracted elements list : "` `+` `str``(res))`

Output

```The original list is : [2, 3, 5, 7, 8, 5, 3, 5]
Extracted elements list : [3, 8, 3]
```

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