How can I optimize this Python code to better performance?

Question

Is there any way to optimize this code?

def find_duplicates(lst):
    duplicates = []
    for i in range(len(lst)):
        for j in range(i + 1, len(lst)):
            if lst[i] == lst[j] and lst[i] not in duplicates:
                duplicates.append(lst[i])
    return duplicates

The code above is already an improvement of another code, but I think it can be improved

Answer 1

You can utilise the collection.Counter class then iterate over its contents to achieve your objective.

The following code identifies items that appear more than once in the list - i.e., not necessarily duplicates

from collections import Counter

def find_duplicates(lst):
    return [k for k, v in Counter(lst).items() if v > 1]

print(find_duplicates([1,2,2,3,4,2,3]))

Output:

[2, 3]