[issue15502] Meta path finders and path entry finders are different, but share an ABC

[Barry A. Warsaw]

Barry A. Warsaw added the comment:

On Aug 02, 2012, at 11:33 AM, Nick Coghlan wrote:

>Specifically, what I did was to drop "find_module" from the Finder ABC, but
>keep the ABC itself as a way to document the common "invalidate_caches"
>API. The ABC definition no longer cares whether you implement find_module()
>or not. MetaPathFinder then enforces find_module(), while PathEntryFinder
>enforces find_loader().

One problem I have, which I'm not sure how to solve, is that the protocol
defines a couple of optional methods, specifically find_loader() on meta path
finders, and module_repr() on loaders.

You'd like for the ABC to be able to capture both the support of these methods
if they exist, and their optional nature, but I don't believe that's possible
with @abc.abstractmethod.  Correct me if I'm wrong, but by adding these
methods to the ABC, it requires subclasses to define them.  I noticed this
when I broke the test suite, and solved it by just adding the methods to the
mocks and other test classes.  But I think this is not the best solution.

Maybe we need an @abc.optionalabstractmethod decorator? ;)

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<http://bugs.python.org/issue15502>
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