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

Brett Cannon brett at python.org
Fri Oct 25 17:40:50 CEST 2013

On Thu, Oct 24, 2013 at 2:05 AM, Eric Snow <ericsnowcurrently at gmail.com>wrote:

I've had some offline discussion with Brett and Nick about PEP 451 which has led to some meaningful clarifications in the PEP. In the interest of pulling further discussions back onto this (archived/public) list, here's an update of what we'd discussed and where things are at. :)

* path entry finders indicate that they found part of a possible namespace package by returning a spec with no loader set (but with submodulesearchlocations set). Brett wanted some clarification on this. * The name/path signature and attributes of file-based finders in importlib will no longer be changing. Brett had some suggestions on the proposed change and it became clear that the the change was actually pointless. * I've asserted that there shouldn't be much difficulty in adjusting pkgutil and other modules to work with ModuleSpec. * Brett asked for clarification on whether the "load()" example from the PEP would be realized implicitly by the import machinery or explicitly as a method on ModuleSpec. This has bearing on the ability of finders to return instances of ModuleSpec subclasses or even ModuleSpec-like objects (a la duck typing). The answer is the it will not be a method on ModuleSpec, so it is effectively just part of the general import system implementation. Finders may return any object that provides the attributes of ModuleSpec. I will be updating the PEP to make these points clear. * Nick suggested writing a draft patch for the language reference changes (the import page). Such a patch will be a pretty good indicator of the impact of PEP 451 on the import system and should highlight any design flaws in the API. This is on my to-do list (hopefully by tomorrow).

Eric's got an initial patch for this up on http://bugs.python.org/issue18864.

* Nick also suggested moving all ModuleSpec methods to a separate class that will simply make use of a separate, existing ModuleSpec instance. This will help address several issues, particularly by relaxing the constraints on what finders can return, but also by avoiding the unnecessary exposure of the methods via every module.spec. I plan on going with this, but currently am trying out the change to see if there are any problems I've missed. Once I feel good about it I'll update the PEP.

That about sums up our discussions. I have a couple of outstanding updates to the PEP to make when I get a chance, as well as putting up a language reference patch for review.

After reading Eric's doc patch, I realized there is one change I want to make to the current semantics and that's not to backfill package when set to None. Since import is now going to take over the job of setting package (along with other attributes), this seems like a slight waste of effort. It also kills (or at least complicates) having a loader which does lazy loading since reading the attribute to see if it is None would trigger the load before leaving the import code, thus killing any postponed loading. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20131025/0c2c8a62/attachment.html>

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