On Mon, 18 May 2015 13:49:45 -0600, Ian Kelly <ian.g.ke...@gmail.com> wrote:
>> Other languages implement slices. I'm currently being faced with a Go >> snippet that mirrors the exact code above and it does run in linear >> time. >> >> Is there any reason why Python 3.4 implementation of slices cannot be >> a near constant operation? > >The semantics are different. IIRC, a slice in Go is just a view of >some underlying array; if you change the array (or some other slice of >it), the change will be reflected in the slice. A slice of a list in >Python, OTOH, constructs a completely independent list. > >It may be possible that lists in CPython could be made to share their >internal arrays with other lists on a copy-on-write basis, which could >allow slicing to be O(1) as long as neither list is modified while the >array is being shared. I expect this would be a substantial piece of >work, and I don't know if it's something that anybody has looked into. This is what I was after. Thank you Ian. So we basically don't have a view of a list. Makes sense now, since slice does create a new list. I should have seen that. Thank you once again. It would a good addition though. Even if only on specialized implementations like pypy. Inspecting and not changing lists is a good chunk of our code. But that's besides the point. I was more interested in understanding the behavior. Thank you once again. -- https://mail.python.org/mailman/listinfo/python-list
