'Lookup playlist with given URI in both the set of playlists and in any
other playlist sources. Returns :class:`None` if not found.
:param uri: playlist URI
:type uri: string
:rtype: :class:`mopidy.models.Playlist` or :class:`None`'

def lookup(self, uri):

    uri_scheme = urllib.parse.urlparse(uri).scheme
    backend = self.backends.with_playlists.get(uri_scheme, None)
    if (not backend):
        return None
    with _backend_error_handling(backend):
        playlist = backend.playlists.lookup(uri).get()
        ((playlist is None) or validation.check_instance(playlist, Playlist))
        return playlist
    return None
