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Finding the index of an element in a list in Python

Programming
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Python
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Operations
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List Operations
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schedule Jul 1, 2022
Last updated
local_offer Python
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We can find the index of an element in a list in Python using either the index(~) method or the enumerate(~) method.

Method

When to use

index(~)

If the list does not contain duplicate items

enumerate(~)

If the list contains duplicate items

Examples

index method

If there are no duplicate elements in the list we can use the index(~) method:

l = ['a', 'b', 'c', 'd']
print(l.index('b'))
1

The index(~) method only returns the position of the first occurrence of an element, hence caution is required if your list contains duplicate items.

If the element does not exist in the list we get a ValueError:

print(l.index('e'))
ValueError: 'e' is not in list

enumerate method

If there are duplicate elements in the list, we can use the enumerate(~) method:

dupe_l = ['a', 'b', 'c', 'd', 'a', 'b']
print([i for i, x in enumerate(dupe_l) if x == 'b'])
[1, 5]

If the element does not exist in the list we return an empty list:

print([i for i, x in enumerate(dupe_l) if x == 'e'])
[]
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Published by Arthur Yanagisawa
Edited by 0 others
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