How to use the xandikos.store.InvalidETag function in xandikos

if uid is not None and self._check_for_duplicate_uids:
            self._scan_uids()
            try:
                (existing_name, _) = self._uid_to_fname[uid]
            except KeyError:
                pass
            else:
                if existing_name != name:
                    raise DuplicateUidError(uid, existing_name, name)

        try:
            etag = self._get_etag(name)
        except KeyError:
            etag = None
        if replace_etag is not None and etag != replace_etag:
            raise InvalidETag(name, etag, replace_etag)
        return etag

:param name: Filename to delete
        :param message: Commit message
        :param author: Optional author
        :param etag: Optional mandatory etag of object to remove
        :raise NoSuchItem: when the item doesn't exist
        :raise InvalidETag: If the specified ETag doesn't match the curren
        """
        path = os.path.join(self.path, name)
        if etag is not None:
            try:
                current_etag = self._get_etag(name)
            except KeyError:
                raise NoSuchItem(name)
            if etag != current_etag:
                raise InvalidETag(name, etag, current_etag)
        try:
            os.unlink(path)
        except EnvironmentError as e:
            if e.errno == errno.ENOENT:
                raise NoSuchItem(path)
            raise

"""
        p = os.path.join(self.repo.path, name)
        try:
            with open(p, 'rb') as f:
                current_blob = Blob.from_string(f.read())
        except IOError:
            raise NoSuchItem(name)
        if message is None:
            fi = open_by_extension(current_blob.chunked, name,
                                   self.extra_file_handlers)
            message = 'Delete ' + fi.describe(name)
        if etag is not None:
            with open(p, 'rb') as f:
                current_etag = current_blob.id
            if etag.encode('ascii') != current_etag:
                raise InvalidETag(name, etag, current_etag.decode('ascii'))
        try:
            with locked_index(self.repo.index_path()) as index:
                os.unlink(p)
                del index[name.encode(DEFAULT_ENCODING)]
                self._commit_tree(index, message.encode(DEFAULT_ENCODING),
                                  author=author)
        except FileLocked:
            raise LockeError(name)

if uid is not None and self._check_for_duplicate_uids:
            self._scan_uids()
            try:
                (existing_name, _) = self._uid_to_fname[uid]
            except KeyError:
                pass
            else:
                if existing_name != name:
                    raise DuplicateUidError(uid, existing_name, name)

        try:
            etag = self._get_etag(name)
        except KeyError:
            etag = None
        if replace_etag is not None and etag != replace_etag:
            raise InvalidETag(name, etag, replace_etag)
        return etag