Zoran Pandovski
By Zoran Pandovski

How to find the index of an element in a list

How to find the index of an element in a list

The list.index method will return the index of the first found element in the list for e.g

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numbers = [1,2,2,2, 3,4,5,6,7]

numbers.index(2)

>>>1

So, in this case, there are 3 elements with value 2 but the index method returns only the first one. If the value is not found index method will raise a ValueError.

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numbers = [1,2,2,2, 3,4,5,6,7]

numbers.index(45)

>>> ValueError: 45 is not in list

The index method will check every element in the list until it finds a match. That means it has O(n) complexity. In the cases where you have a very long list, you can consider using the start or end optional parameters to the index for e.g

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numbers = [1,2,3,4,5,6,7,8,9,10,11,12]

# find index of 11 starting from 9th element

numbers.index(11, 9)

>>>10