[Python-Dev] Choosing a best practice solution for Python/extension modules (original) (raw)

Brett Cannon brett at python.org
Mon Feb 23 20:02:46 CET 2009

On Sun, Feb 22, 2009 at 22:41, Aahz <aahz at pythoncraft.com> wrote:

On Sun, Feb 22, 2009, Brett Cannon wrote: > On Sat, Feb 21, 2009 at 20:12, Aahz <aahz at pythoncraft.com> wrote: >> On Sat, Feb 21, 2009, Brett Cannon wrote: >>> On Sat, Feb 21, 2009 at 15:46, Aahz <aahz at pythoncraft.com> wrote: >>>> On Sat, Feb 21, 2009, Brett Cannon wrote: >>>>> >>>>> I am seeing two approaches emerging. One is where pickle contains all >>>>> Python code and then uses something like useextension to make sure >>>>> the original Python objects are still reachable at some point. This >>>>> has the drawback that you have to use some function to make the >>>>> extensions happen and there is some extra object storage. >>>>> >>>>> The other approach is having pickle contain code known not to >>>>> be overridden by anyone, import pypickle for stuff that may be >>>>> overridden, and then import pickle for whatever is available. This >>>>> approach has the perk of using a standard practice for how to pull in >>>>> different implementation. But the drawback, thanks to how globals are >>>>> bound, is that any code pulled in from pickle/pypickle will not be >>>>> able to call into other optimized code; it's a take or leave it once >>>>> the call chain enters one of those modules as they will always call >>>>> the implementations in the module they originate from. >>>> >>>> To what extent do we care about being able to select Python-only on a >>>> per-module basis, particularly in the face of threaded imports? That >> is, >>>> we could have a sys.pythononly attribute that gets checked on import. >>>> That's simple and direct, and even allows per-module switching if the >>>> application really cares and import doesn't need to worry about threads. >>>> >>>> Alternatively, sys.pythononly could be a set, but that gets ugly about >>>> setting from the application. (The module checks to see whether it's >>>> listed in sys.pythononly.) >>>> >>>> Maybe we should move this discussion to python-ideas for now to kick >>>> around really oddball suggestions? >>> >>> This is all about testing. If a change is made to some extension code it >>> should be mirrored in the Python code and vice-versa. >> >> Okay, I don't see how that is a response to my suggestion -- I can >> imagine that someone might want to test a combination of pure-Python and >> binary libraries. > > I don't want to move it because this isn't some idea for a new feature that > may or may not be useful; this isn't an "idea", it's needed.

That's fine, but what about my idea of using sys.pythononly?

But what is it supposed to represent? That only pure Python modules get imported? What if the module depends on another module that is an extension module?

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