Hi Mike, On 20 January 2015 at 05:26, Mike Kaplinskiy <mike.kaplins...@gmail.com> wrote: > https://bitbucket.org/mikekap/pypy/commits/b774ae0be11b2012852a175f4bae44841343f067 > has an implementation of list slicing that copies the data on write. (The > third idea from http://doc.pypy.org/en/latest/project-ideas.html .)
One hard bit about implementing this kind of change is making sure you don't accidentally slow some other kinds of code down. This requires running all our benchmarks, at least, as fijal pointed out. Here are some additional issues to consider. We have to consider the overhead in terms of memory usage: it's probably fine if the overhead is only one pointer per list object (which often points to some fixed tuple like (0, None, None)). However, if you do "x = large_list[5:7]" you keep the whole "large_list" alive as long as "x" is alive. This might be an issue for some cases. Resolving it is possible but more involved. It would probably require GC support --- i.e. we can't really solve this nicely in regular RPython as it is now. The details need discussion, but I can think for example about a way to tell the GC "this is a pointer to the full list, but I'm only going to access this range of items, so ignore the rest". Another way would be to have some callback that copies just the items needed out of the large list, but that's full of open questions... A bientôt, Armin. _______________________________________________ pypy-dev mailing list pypy-dev@python.org https://mail.python.org/mailman/listinfo/pypy-dev
