[Python] How to implement an import hook that can modify the source code on the fly using...

Using the deprecated module imp, I can write a custom import hook that modifies the source code of a module on the fly, prior to importation/execution by Python. Given the source code as a string named source below, the essential code needed to create a module is the following:

module = imp.new_module(name)
sys.modules[name] = module
exec(source, module.__dict__)


Since imp is deprecated, I would like to do something similar with importlib. [EDIT: there are other imp methods that need to be replaced to build a custom import hook - so the answer I am looking for is not simply to replace the above code.]

However, I have not been able to figure out how to do this. The importlib documentation has a function to create modules from "specs" which, as far as I can tell, are objects that include their own loaders with no obvious way to redefine them so as to be able to create a module from a string.

I have created a minimal example to demonstrate this; see the README file for details.

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