Avoid import-time dependency on typing in common cases
#329
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…me usage of typing constructs (in this case, Protocol).
…urces.abc to 1) publicly export Traversable from importlib_resources._traversable and 2) use Traversable in internal annotations, all without importing it eagerly at import time.
…s been removed from importlib_resources.abc, do the same for importlib_resources._common by avoiding typing.cast and avoiding eager import and execution of symbols from importlib_resources.abc.
…ols. This will be used shortly to avoid import-time typing imports in importlib_resources_common and importlib_resources.abc.
…e previously created _typing shim in conjunction with deferred annotations. This way, importlib_resources.abc never imports typing at import time.
… import annotations is active.
…g the previously created _typing shim in conjunction with deferred annotations. This way, importlib_resources._common never imports typing at import time.
…tions to complement the __getattr__ functions. Also, improve __getattr__ comments and ensure those functions have the same structure.
…ces.__init__, since that's where it's eagerly imported from.
…s._common to not use functools.singledispatch, since singledispatch will always import typing.
typing in common cases
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Part of #326.
Overview
typingas a import-time dependency can be avoided for most of this library's use cases through a combination of the following:typing.functools.singledispatchtypingat import time, so that importing them is opt-in.importlib_resources.abc.Traversable__getattr__.This way, when importing just the base or functional API (
files(),as_file(),open_binary, etc.), which I imagine is a very common use case, users don't also importtypingimmediately as a side-effect. This will improve the import time ofimportlib_resourcesfor such common cases by at least 10%, possibly more, while still having the type annotations be valid and resolve to the correct symbols when introspected/evaluated.This PR's intended viewing is commit by commit, in order.
Notes
I'm guessing this one will be a bit more controversial than the other PRs due to refactoring away usage of
functools.singledispatch, but if we want to usetypingwithout incurring its import cost on multiple Python versions, I think it's easiest to just avoidsingledispatchaltogether inimportlib_resources._common.singledispatchusage is also a potential blocker for possible future improvements, e.g. lazily importingpathlib.Path.That being said, I'll try to see if there's a way to use
singledispatchfor the moment without it unconditionally importingtyping. Doing so would rely on implementation details and thus be fragile at best, so I'm not a fan of it.