[Python-Dev] PEP 451 update (original) (raw)

Eric Snow ericsnowcurrently at gmail.com
Wed Oct 30 23:54:13 CET 2013

On Wed, Oct 30, 2013 at 4:09 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

On 31 Oct 2013 03:41, "Eric Snow" <ericsnowcurrently at gmail.com> wrote:

Our recent discovery about reloading should probably be reflected in the signature of finder.findspec():

MetaPathFinder.findspec(name, path=None, existing=None) PathEntryFinder.findspec(name, existing=None) This way the finder has an opportunity to incorporate information from an existing spec into the spec it returns. reload() would make use of this by passing module.spec (or None if the module has no spec) to bootstrap.findspec(). This approach should also address what you are looking for. I'd prefer it over passing the existing spec to execmodule(). The module (and its spec) should have everything execmodule() needs to do its job. Yes, that should work.

Cool. I'll update the PEP.

We would still need to use loader.supportsreload() in reload(). Why? If the reload isn't supported, execmodule can just throw an exception based on the loader state in the spec.

At the point that exec_module() gets called, the loader can't check sys.modules to see if it's a reload or not. As a workaround, the finder could set up some loader state to indicate to the loader that it's a reload and then the loader, during exec_module(), would check that and act accordingly. However, that's the sort of boilerplate that PEP 451 is trying to offload onto the import machinery. With Loader.supports_reload() it's a lot cleaner.

-eric

From the import system's point of view "reload not permitted" is no different from any other exec time failure. Cheers, Nick.

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