Find the relative path from here from the parent_dir

def relpath_for(self, path):
        """Find the relative path from here from the parent_dir"""
        if self.parent_dir in (".", ""):
            return path

        if path == self.parent_dir:
            return ""

        dirname = os.path.dirname(path) or "."
        basename = os.path.basename(path)

        cached = self.relpath_cache.get(dirname, empty)
        if cached is empty:
            cached = self.relpath_cache[dirname] = os.path.relpath(dirname, self.parent_dir)

        return os.path.join(cached, basename)