(mostly stuff specified by PEP 302). There are two ABCs, PyLoader and
PyPycLoader, which help with implementing source and source/bytecode loaders by
implementing load_module in terms of other methods. This removes a lot of
gritty details loaders typically have to worry about.
+ Ditch using arguments to super().
+ Ditch subclassing from object directly.
+ Move directory check out of chaining path hook to file path hook/finder.
+ Rename some classes to better reflect they are finders, not importers.
case-insensitive file system, leading to test failures. This was due to using
the TestCase objects directly instead of the guard in the test_main() function.
Move over to a class decorator instead to control if the tests should be run.