Modernize the importlib loaders

[FFY00]

BPO	45547
Nosy	@warsaw, @brettcannon, @jaraco, @ncoghlan, @ericsnowcurrently, @FFY00

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assignee = None
closed_at = None
created_at = <Date 2021-10-20.23:15:10.249>
labels = []
title = 'Modernize the importlib loaders'
updated_at = <Date 2021-10-21.21:24:44.368>
user = 'https://github.com/FFY00'

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activity = <Date 2021-10-21.21:24:44.368>
actor = 'brett.cannon'
assignee = 'none'
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creation = <Date 2021-10-20.23:15:10.249>
creator = 'FFY00'
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issue_num = 45547
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url = 'https://bugs.python.org/issue45547'
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[FFY00]

ResourceLoader[1] is deprecated in favor of ResourceReader, which itself is surpassed by TraversableResources.

Would it make sense to replace ResourceLoader usages with ResourceReader in the importlib loaders?
And perhaps, would it make sense to replace them with the files()/Traversable protocol instead?

IMO this could simplify the code a bit, but that's subjective I guess, and better re-use the bytecode caching mechanism in SourceLoader, by providing an equivalent based on files()/Traversable instead.

This could also help push to add support for non filesystem based loaders in other parts of the code, like py_compile, which currently only supports operations on the filesystem.

Is this something we are interested in -- modernizing the importlib loaders with, arguably, better abstractions -- or do we want to keep the old protocols around?

[1] https://docs.python.org/3/library/importlib.html#importlib.abc.ResourceLoader

[brettcannon]

It's an interesting question. Probably should add the new APIs. As for dropping the old ones, we would have to check if we have been raising deprecation warnings as appropriate or if it's just a documentation thing.