How to find the last occurrence of an item in a Python list

user_697529 0
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Say I have this list:

li = ["a", "b", "a", "c", "x", "d", "a", "6"]

As far as help showed me, there is not a builtin function that returns the last occurrence of a string (like the reverse of index). So basically, how can I find the last occurrence of "a" in the given list?

last-occurrence list python
15 Answers

With dict

You can use the fact that dictionary keys are unique and when building one with tuples only the last assignment of a value for a particular key will be used. As stated in other answers, this is fine for small lists but it creates a dictionary for all unique values and might not be efficient for large lists.

dict(map(reversed, enumerate(li)))["a"]

6
user_23366540 
lastIndexOf = lambda array, item: len(array) - (array[::-1].index(item)) - 1
user_117148600

Love @alcalde's solution, but faced ValueError: max() arg is an empty sequence if none of the elements match the condition.

To avoid the error set default=None:

max((loc for loc, val in enumerate(li) if val == 'a'), default=None)
user_91109550

val = [1,2,2,2,2,2,4,5].

If you need to find last occurence of 2

last_occurence = (len(val) -1) - list(reversed(val)).index(2)

user_27825610

If the list is small, you can compute all indices and return the largest:

index = max(i for i, x in enumerate(elements) if x == 'foo')
user_10791100
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