Tuple slices

[George Sakkis]

"Jeff Shannon" <jeff at ccvcorp.com> wrote in message news:10vb3enf8qvld4 at corp.supernews.com...
> [My newsreader crapped out on sending this; apologies if it appears
> twice.]
>
> George Sakkis wrote:
>
> > "Terry Reedy" <tjreedy at udel.edu> wrote in message
> > news:mailman.1226.1106605134.22381.python-list at python.org...
> >
> >>Aside from the problem of not being able to delete the underlying object,
> >>the view object for a tuple would have to be a new type of object with a
> >>new set of methods.
> >
> > It *could*, but it doesn't have to. One can represent a view as essentially an object with a
pointer
> > to a memory buffer and a (start,stop,step) triple. Then a "real tuple" is just a "view" with the
> > triple being (0, len(sequence), 1).
>
> Except that that's not how Python tuples *are* constructed, and it'd
> be a pretty big deal to redo the architecture of all tuples to support
> this relatively special case.
>
> Even if this re-architecting were done, you're still constructing a
> new object -- the difference is that you're creating this
> (start,stop,step) triple instead of duplicating a set of PyObject*
> pointers, and then doing math based on those values instead of
> straightforward pointer access.  I'm not at all convinced that this
> really saves you a significant amount for tuple slices (really, you're
> still constructing a new tuple anyhow, aren't you?), and it's going to
> cost a bit in both execution time and complexity in the common case
> (accessing tuples without slicing).  If there's a big cost in object
> construction, it's probably going to be the memory allocation, and for
> a reasonable tuple the size of the memory required is not going to
> significantly affect the allocation time.
>
> Jeff Shannon
> Technician/Programmer
> Credit International
>

You're probably right about the allocation time, but my main concern is the memory required for each
slice, which can be O(n) wrt the length of the whole tuple. I would like this to be constant (at
least if there was a way around to the problem of deleting the underlying sequence).

George