# Python – Replace all repeated occurrences with N

• Last Updated : 09 Mar, 2020

Sometimes, while working with Python list, we can have a problem in which we need to replace an element with another. But one can have variations of these such as increase of number and keeping the first occurrence. This can have applications in various domains. Lets discuss certain ways in which this task can be performed.

Method #1 : Using `enumerate() + set()` + loop
The combination of above functions can be used to perform this task. In this, we iterate the list and then store the 1st occurrence in set, the consecutive values are tested using in and replaced inplace.

 `# Python3 code to demonstrate ``# Replace all repeated occurrences of K with N``# using enumerate() + set() + loop`` ` `# Initializing list``test_list ``=` `[``1``, ``3``, ``3``, ``1``, ``4``, ``4``, ``1``, ``5``, ``5``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Initializing N ``N ``=` `'rep'`` ` `# Replace all repeated occurrences of K with N``# using enumerate() + set() + loop``his ``=` `set``([])``for` `idx, ele ``in` `enumerate``(test_list):``    ``if` `ele ``in` `his:``        ``test_list[idx] ``=` `N``    ``his.add(ele)`` ` `# printing result ``print` `(``"The duplication altered list : "` `+` `str``(test_list))`

Output :

```The original list is : [1, 3, 3, 1, 4, 4, 1, 5, 5]
The duplication altered list : [1, 3, 'rep', 'rep', 4, 'rep', 'rep', 5, 'rep']
```
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