this post was submitted on 12 Apr 2025
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195
Python Performance: Why 'if not list' is 2x Faster Than Using len() (blog.codingconfessions.com)
submitted 1 week ago by abhi9u@lemmy.world to c/technology@lemmy.world
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[–] borokov@lemmy.world 2 points 1 week ago (1 children)

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)
[–] riodoro1@lemmy.world 2 points 1 week ago (1 children)

That’s exactly what I was getting at. Getting length of an empty list would not even enter the loop.

[–] ChaoticNeutralCzech@feddit.org 1 points 1 week ago

Yes. If it's empty. But in cases where you need to check, it might as well not be.