This past week a lot of people have asked me about how to set up an importer. It's enough to warrant adding an example in the new Examples section of the importlib docs to explain how to do this using the pre-existing classes in importlib.machinery for illustrative  purposes.

New changeset dc24ab548e2b by Brett Cannon in branch 'default':
Issue #26252: Add an example on how to register a finder
https://hg.python.org/cpython/rev/dc24ab548e2b

I added an example on how to register both a meta path and path entry finder. It's a rather simple example, but hopefully using the classes that importlib uses will help also point people towards the appropriate classes to learn about for their own needs.