The len(pics) can be O(n), especially if iterators are used like here. Also, an O(1) lookup would require a previous O(n) pass over the data anyway. The pictur

The len(pics) can be O(n), especially if iterators are used like here. Also, an O(1) lookup would require a previous O(n) pass over the data anyway. The picture selection algorithm's kind of single-pass iterator usage might have been more performant back in the XP days, as it avoids possibly expensive operations. Modern CPU/other optimizations might make a multi-pass approach more performant due to better memory locality or other factors.