If here test the namespace module in zip, mkdir() must be removed, this bug is triggered by no directory entry in zip.

And don't do test via zipimport, that always fail/succeed, because find functons depend the loader's path prefix. Direct import namespace module can cover all cases.

I'm a bit confused on what you want here - the test passes, why should mkdir() be removed?

Again, this bug is triggered by no directory entry in zip. If the directory entry is already exists, everything is OK.

As https://github.com/python/cpython/pull/121161/files#r1660062444 described, this patch has no effect, shoud patch _is_dir or _read_directory.

As https://github.com/python/cpython/pull/121161/files#r1660062444 described, this patch has no effect, shoud patch _is_dir or _read_directory.

From what I found, there's no problem with _read_directory, and _is_dir is only relevant to find_spec (the problem still occurs in get_code, for example). This patch seems to fix the issue for both. Have you tried this fix on this issue?

For namespace package's dealing and operation, there has already clearly explained in the source code comment. You can see them in find_loader (<=py311), find_spec and _is_dir.

And, why your test with get_code (and get_filename, get_source, is_package also) was fail? Because find functons depend the loader's path prefix, different level modules have different level loaders, skip levels will be failed. Yes, this is _get_module_path which you patched, then it broken, return the full path at once instead of stepwise lookup.

If you like to test into zipimport functions, it should be get_data:

    def testImportSubmodulesInZip(self):
        with ZipFile(TEMP_ZIP, "w") as z:
            z.writestr("a/__init__.py", b'')
            z.writestr("a/b/c/__init__.py", b'def foo(): return "foo"')

        importer = zipimport.zipimporter(TEMP_ZIP + "/a/")
        spec = importer.find_spec("a.b")
        self.assertEqual(spec.loader, None)
        self.assertEqual(spec.submodule_search_locations,
                         [(TEMP_ZIP + "/a/b").replace("/", zipimport.path_sep)])
        self.assertRaises(zipimport.ZipImportError, importer.get_code, "a.b")
        self.assertEqual(importer.get_data("a/b/"), b"")

        sys.path.insert(0, TEMP_ZIP)
        try:
            import a.b.c
            self.assertIn('namespace', str(a.b).lower())
            self.assertEqual(a.b.c.foo(), "foo")
        finally:
            del sys.path[0]
            sys.modules.pop('a.b.c', None)
            sys.modules.pop('a.b', None)
            sys.modules.pop('a', None)

I agree with @SeaHOH that the problem is rather in _read_directory(). I created #121233 for this approach.