Dummy importlib-based importer sample

loader_sample.py

from importlib.abc import PathEntryFinder, SourceLoader, FileLoader
from importlib.util import module_for_loader

class MyFinder(PathEntryFinder):
    def __init__(self, pathentry):
        """Create a finder for the given `pathentry`"""
        if pathentry == 'foo':
            return
        raise ImportError
    def find_loader(self, fullname):
        """Return a loader for the module `fullname`"""
        print("find_loader('{}')".format(fullname))
        return MyLoader(fullname, 'foo/__init__.py'), ['foo']

class MyLoader(FileLoader, SourceLoader):
    def module_repr(self):
        return "!!!"
    def get_data(self, path):
        """Return an open binary file object for `path`"""
        print("get_data('{}')".format(path))
        return b"print('hello from foo!')"

if __name__ == '__main__':
    import sys
    sys.path_hooks.append(lambda p: MyFinder(p))
    sys.path.insert(0, 'foo')
    import a
    import a.b
    from a.b.c import x