I don't know if this is a necessary test case for get_data, maybe directory path will be never passed to it.

I see the ImportHooksBaseTestCase has setUp and tearDown to restore the environ, so the finally section could be removed.

I probably would have written this as something like:

    files.update(dict.fromkeys(zipfile._path.CompleteDirs._implicit_dirs(files)))

(or some variation that ports the CompleteDirs._implicit_dirs without itertools). The advantages of using that implementation are:

• it's a proven implementation and has already encountered real-world edge cases
• it uses lazy evaluation to ensure compact memory usage
• it applies functional principles, avoiding mutating structures in place and simplifying the logic

If you want the count of files added:

    updates = dict.fromkeys(zipfile._path.CompleteDirs._implicit_dirs(files))
    files.update(updates)
    count = len(updates)

Of course, CompleteDirs operates on posixpath.sep and files here uses pathsep for separators, so maybe it's not worth porting CompleteDirs. Still, I think it would be nice if this new behavior were factored out so as to limit making this already enormous function much larger.

I set out to apply this approach in #121378.