Comment on Python Performance: Why 'if not list' is 2x Faster Than Using len()
riodoro1@lemmy.world 3 days agoSo… it has to iterate over the whole empty list is what you’re saying? like once for every of the zero items in the lost?
Don’t know how list are implemented in Python. But in the dumb linked list implementation (like C++ std::list), each element has a “next” member that point the the next element. So, to have list length, you have to do (pseudo code, not actual python code):
len = 0 elt = list.fisrt while exist(elt): elt = elt.next len++ return len
Whereas to test if list is empty, you just have to:
return exist(list.first)
That’s exactly what I was getting at. Getting length of an empty list would not even enter the loop.
Yes. If it’s empty. But in cases where you need to check, it might as well not be.
ChaoticNeutralCzech@feddit.org 3 days ago
The list is not necessarily empty. If you were sure it was, why check?