How to use the vdirsyncer.utils.get_etag_from_file function in vdirsyncer

def list(self):
        self._items = collections.OrderedDict()

        try:
            self._last_etag = get_etag_from_file(self.path)
            with open(self.path, self._read_mode) as f:
                text = f.read().decode(self.encoding)
        except OSError as e:
            import errno
            if e.errno != errno.ENOENT:  # file not found
                raise OSError(e)
            text = None

        if not text:
            return ()

        for item in split_collection(text):
            item = Item(item)
            etag = item.hash
            self._items[item.ident] = item, etag

def delete(self, href, etag):
        fpath = self._get_filepath(href)
        if not os.path.isfile(fpath):
            raise exceptions.NotFoundError(href)
        actual_etag = get_etag_from_file(fpath)
        if etag != actual_etag:
            raise exceptions.WrongEtagError(etag, actual_etag)
        os.remove(fpath)

def _write(self):
        if self._last_etag is not None and \
           self._last_etag != get_etag_from_file(self.path):
            raise exceptions.PreconditionFailed((
                'Some other program modified the file {!r}. Re-run the '
                'synchronization and make sure absolutely no other program is '
                'writing into the same file.'
            ).format(self.path))
        text = join_collection(
            item.raw for item, etag in self._items.values()
        )
        try:
            with atomic_write(self.path, mode='wb', overwrite=True) as f:
                f.write(text.encode(self.encoding))
        finally:
            self._items = None
            self._last_etag = None

def _upload_impl(self, item, href):
        fpath = self._get_filepath(href)
        try:
            with atomic_write(fpath, mode='wb', overwrite=False) as f:
                f.write(item.raw.encode(self.encoding))
                return fpath, get_etag_from_file(f)
        except OSError as e:
            if e.errno == errno.EEXIST:
                raise exceptions.AlreadyExistingError(existing_href=href)
            else:
                raise

def update(self, href, item, etag):
        fpath = self._get_filepath(href)
        if not os.path.exists(fpath):
            raise exceptions.NotFoundError(item.uid)
        actual_etag = get_etag_from_file(fpath)
        if etag != actual_etag:
            raise exceptions.WrongEtagError(etag, actual_etag)

        if not isinstance(item.raw, str):
            raise TypeError('item.raw must be a unicode string.')

        with atomic_write(fpath, mode='wb', overwrite=True) as f:
            f.write(item.raw.encode(self.encoding))
            etag = get_etag_from_file(f)

        if self.post_hook:
            self._run_post_hook(fpath)
        return etag

def update(self, href, item, etag):
        fpath = self._get_filepath(href)
        if not os.path.exists(fpath):
            raise exceptions.NotFoundError(item.uid)
        actual_etag = get_etag_from_file(fpath)
        if etag != actual_etag:
            raise exceptions.WrongEtagError(etag, actual_etag)

        if not isinstance(item.raw, str):
            raise TypeError('item.raw must be a unicode string.')

        with atomic_write(fpath, mode='wb', overwrite=True) as f:
            f.write(item.raw.encode(self.encoding))
            etag = get_etag_from_file(f)

        if self.post_hook:
            self._run_post_hook(fpath)
        return etag

def get(self, href):
        fpath = self._get_filepath(href)
        try:
            with open(fpath, 'rb') as f:
                return (Item(f.read().decode(self.encoding)),
                        get_etag_from_file(fpath))
        except OSError as e:
            if e.errno == errno.ENOENT:
                raise exceptions.NotFoundError(href)
            else:
                raise