[Import-SIG] Round 2 for "A ModuleSpec Type for the Import System"

[Brett Cannon]

On Tue, Aug 13, 2013 at 12:17 AM, Eric Snow <ericsnowcurrently at gmail.com>wrote:

> On Sun, Aug 11, 2013 at 2:08 PM, Brett Cannon <brett at python.org> wrote:
>
>>
>>
[SNIP]


>
>>
>>>  ``module_repr()`` also conflicts with the same
>>> method on loaders, but that workaround is not complicated since both are
>>> methods.
>>>
>>> Unfortunately, the ability to proxy does not extend to ``id()``
>>> comparisons and ``isinstance()`` tests.  In the case of the return value
>>> of ``find_module()``, we accept that break in backward compatibility.
>>> However, we will mitigate the problem with ``isinstance()`` somewhat by
>>> registering ``ModuleSpec`` on the loaders in ``importlib.abc``.
>>>
>>
>> Actually, ModuleSpec doesn't even need to register; __instancecheck__ and
>> __subclasscheck__ can just be defined and delegate by calling
>> issubclass/isinstance on the loader as appropriate.
>>
>
> Do you mean add custom versions of those methods to importlib.abc.Loader?
>

Nope, I meant ModuleSpec because every time I have a reason to override
something it's on the object and not the class and so I forget the support
is the other way around. Argh.


>  That should work as well as the register approach.  It won't work for all
> loaders but should be good enough.  I was just planning on registering
> ModuleSpec on the loader in the setter for a `loader` property on
> ModuleSpec.
>

But the registration is at the class level so how would that work?
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