def list_duplicates(cells):
    """Find duplicates in list for detailed reporting
    """
    # reference https://stackoverflow.com/questions/9835762
    seen = set()
    # save add function to avoid repeated lookups
    seen_add = seen.add
    # list comprehension below chosen for computational efficiency
    # adds all new elements to seen and all other to seen_twice
    # 'or' allows seen_add(x) evaluation only if x is not in seen
    seen_twice = set(x for x in cells if x in seen or seen_add(x))
    return list(seen_twice)