Isn’t it because list is linked list, so to get the Len it has to iterate over the whole list whereas to get emptyness it just have to check if there is a 1st element ?
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.nextlen++
returnlen
Whereas to test if list is empty, you just have to:
Isn’t it because list is linked list, so to get the Len it has to iterate over the whole list whereas to get emptyness it just have to check if there is a 1st element ?
I’ too lazy to read the article BTW.
No,
lenis a constant time operation, at least in most cases I believe.Then please be less lazy next time.
So… it has to iterate over the whole empty list is what you’re saying? like once for every of the zero items in the list?
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 lenWhereas 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.
The list is not necessarily empty. If you were sure it was, why check?