[Python-Dev] Update on PEP 523 and adding a co_extra field to code objects (original) (raw)

Brett Cannon brett at python.org
Tue Aug 30 14:12:01 EDT 2016

On Tue, 30 Aug 2016 at 10:49 Antoine Pitrou <solipsis at pitrou.net> wrote:

On Tue, 30 Aug 2016 17:35:35 +0000 Brett Cannon <brett at python.org> wrote: > > > > Perhaps a list would work indeed. Realistically, if there are at most > > 2-3 users of the field at any given time (and most probably only one or > > zero), a simple type check (by pointer equality) on each list item may > > be sufficient. > > > > Let's see what Maciej says, but we could standardize on switching the field > to a list when a conflict of usage is detected so the common case in the > frame eval function is checking for your own type, and if that fails then > doing a PyListCheckExact() and look for your object, otherwise make a list > and move over to that for everyone to use. A little bit more code, but it's > simple code and takes care of conflicts only when it calls for it.

That's a bit obscure and confusing, though (I think the weakref module uses a similar kludge in some place). If you want to iterate on it you have to write some bizarre macro to share the loop body between the two different code-paths (list / non-list), or some equally tedious function-pointer-based code.

I don't quite follow where the complexity you're suggesting comes from. The frame evaluation function in Pyjion would just do:

if (co_extra == NULL) { // No one using the field. co_extra = pyjion_cache = PyPyjion_New(); } else if (!is_pyjion_object(co_extra)) { // Someone other than us is using the field. if (PyList_CheckExact(co_extra)) { // Field is already a list. ... look for object ... if (ob_found != NULL) { // We're in the list. pyjion_cache = ob_found; } else { // Not in the list, so add ourselves. pyjion_cache = PyPyjion_New(); co_extra.append(pyjion_cache); } } else { // Someone else in the field, not a list (yet). other_ob = co_extra; co_extra = PyList_New(); co_extra.append(other_ob); pyjion_cache = PyPyjion_New(); co_extra.append(pyjion_cache); } } else { // We're in the field. pyjion_cache = co_extra; }

Why not make it always a list? List objects are reasonably cheap in memory and access time... (unlike dicts)

Because I would prefer to avoid any form of unnecessary performance overhead for the common case. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160830/68ce54ef/attachment.html>

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