[Python-Dev] Require loaders set __package__ and __loader__

Andrew Svetlov andrew.svetlov at gmail.com
Wed Apr 18 00:38:50 CEST 2012

+1 for initial proposition.

On Tue, Apr 17, 2012 at 6:59 PM, Brett Cannon <brett at python.org> wrote:
> Anyone other than Eric have something to say on this proposal? Obviously the
> discussion went tangential before I saw a clear consensus that what I was
> proposing was fine with people.
> On Sat, Apr 14, 2012 at 16:56, Brett Cannon <brett at python.org> wrote:
>> An open issue in PEP 302 is whether to require __loader__ attributes on
>> modules. The claimed worry is memory consumption, but considering importlib
>> and zipimport are already doing this that seems like a red herring.
>> Requiring it, though, opens the door to people relying on its existence and
>> thus starting to do things like loading assets with
>> ``__loader__.get_data(path_to_internal_package_file)`` which allows code to
>> not care how modules are stored (e.g. zip file, sqlite database, etc.).
>> What I would like to do is update the PEP to state that loaders are
>> expected to set __loader__. Now importlib will get updated to do that
>> implicitly so external code can expect it post-import, but requiring loaders
>> to set it would mean that code executed during import can rely on it as
>> well.
>> As for __package__, PEP 366 states that modules should set it but it isn't
>> referenced by PEP 302. What I want to do is add a reference and make it
>> required like __loader__. Importlib already sets it implicitly post-import,
>> but once again it would be nice to do this pre-import.
>> To help facilitate both new requirements, I would update the
>> importlib.util.module_for_loader decorator to set both on a module that
>> doesn't have them before passing the module down to the decorated method.
>> That way people already using the decorator don't have to worry about
>> anything and it is one less detail to have to worry about. I would also
>> update the docs on importlib.util.set_package and importlib.util.set_loader
>> to suggest people use importlib.util.module_for_loader and only use the
>> other two decorators for backwards-compatibility.
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Andrew Svetlov

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