# Python | Find indices with None values in given list

Many times while working in data science domain we need to get the list of all the indices which are None, so that they can be easily be prepossessed. This is quite a popular problem and solution to it comes quite handy. Let’s discuss certain ways in which this can be done.

Method #1 : Using list comprehension + `range()`
In this method we just check for each index using the range function and store the index if we find that index is None.

 `# Python3 code to demonstrate ` `# finding None indices in list  ` `# using list comprehension + enumerate ` ` `  `# initializing list  ` `test_list ``=` `[``1``, ``None``, ``4``, ``None``, ``None``, ``5``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using list comprehension + enumerate ` `# finding None indices in list  ` `res ``=` `[i ``for` `i ``in` `range``(``len``(test_list)) ``if` `test_list[i] ``=``=` `None``] ` ` `  `# print result ` `print``(``"The None indices list is : "` `+` `str``(res)) `

Output :

```The original list : [1, None, 4, None, None, 5]
The None indices list is : [1, 3, 4]
```

Method #2 : Using list comprehension + `enumerate()`
The enumerate function can be used to iterate together the key and value pair and list comprehension can be used to bind all this logic in one line.

 `# Python3 code to demonstrate ` `# finding None indices in list  ` `# using list comprehension + enumerate ` ` `  `# initializing list  ` `test_list ``=` `[``1``, ``None``, ``4``, ``None``, ``None``, ``5``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using list comprehension + enumerate ` `# finding None indices in list  ` `res ``=` `[i ``for` `i, val ``in` `enumerate``(test_list) ``if` `val ``=``=` `None``] ` ` `  `# print result ` `print``(``"The None indices list is : "` `+` `str``(res)) `

Output :

```The original list : [1, None, 4, None, None, 5]
The None indices list is : [1, 3, 4]
```

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.