Reference library

Lists & loops

Iterate, transform, and combine sequences with readable loop patterns.

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Lists & loops easy

Find Duplicate Elements in a Python List

Identifies and returns duplicate elements from a Python list using sets for efficient membership tests.

duplicates sets list
Python 
def find_duplicates(lst):
    seen = set()
    duplicates = set()
    for item in lst:
        if item in seen:
            duplicates.add(item)
        else:
            seen.add(item)
    return list(duplicates)

if __name__ == "__main__":
    sample = [1, 2, 3, 2, 4, 1, 5, 3]
    print(find_duplicates(sample))
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Lists & loops — Python code examples

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