def METHOD_NAME() -> Dict[str, List[str]]:
    ext_map = {}
    for typ_ in filetypes:
        cls = get_dataset_cls(typ_)
        for ext in cls.get_supported_extensions():
            try:
                ext_map[ext].append(typ_)
            except KeyError:
                ext_map[ext] = [typ_]
    return ext_map