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Python – Replace Non-None with K
• Last Updated : 03 Jul, 2020

Sometimes, while working with Python lists we can have a problem in which we need to perform the replacment of all the elements that are non-None. This kind of problem can have application in many domains such as web development and day-day programming. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [2, None, None, 5, ”], K = 9
Output : [9, None, None, 9, ”]

Input : test_list = [”, None], K = 10
Output : [”, None]

Method #1 : Using list comprehension
This is one of the ways in which this task can be performed. In this, we perform the task of traversing and replacement inside comprehension as one liner using conditions.

 `# Python3 code to demonstrate working of ``# Replace Non-None with K``# Using list comprehension`` ` `# initializing list``test_list ``=` `[``59``, ``236``, ``None``, ``3``, '']`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing K ``K ``=` `'Gfg'`` ` `# Replace Non-None with K``# Using list comprehension``res ``=` `[K ``if` `ele ``else` `ele ``for` `ele ``in` `test_list]``         ` `# printing result ``print``(``"List after replacement : "` `+` `str``(res))`
Output :

```The original list : [59, 236, None, 3, '']
List after replacement : ['Gfg', 'Gfg', None, 'Gfg', '']
```

Method #2 : Using `map() + lambda()`
The combination of above functions can be used to solve this problem. In this, we perform the task of extending lambda logic to entire list using map() and perform replacement.

 `# Python3 code to demonstrate working of ``# Replace Non-None with K``# Using map() + lambda()`` ` `# initializing list``test_list ``=` `[``59``, ``236``, ``None``, ``3``, '']`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# initializing K ``K ``=` `'Gfg'`` ` `# Replace Non-None with K``# Using map() + lambda()``res ``=` `list``(``map``(``lambda` `ele: K ``if` `ele ``else` `ele, test_list))``         ` `# printing result ``print``(``"List after replacement : "` `+` `str``(res))`
Output :
```The original list : [59, 236, None, 3, '']
List after replacement : ['Gfg', 'Gfg', None, 'Gfg', '']
```

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