Kivy Experimental not working unfinished radargraph

gistfile1.txt

from math import cos, sin, pi

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Color, Ellipse, Line, Mesh
from kivy.properties import ListProperty
from kivy.clock import Clock

import itertools
import random

class RadarGraph(Widget):
    datas = ListProperty()

    def __init__(self,):
        Widget.__init__(self, )
        self.bind(datas=self.redraw)
        Clock.schedule_once(self.on_touch_down, 1)

    def on_touch_down(self, touch):
        self.datas = [random.random() for i in range(5)]

    def redraw(self, *args):
        if len(self.datas) < 0:
            return

        self.canvas.clear()
        angle = 2*pi / len(self.datas)
        rayon = min(self.center_x * 0.9, self.center_y * 0.9)
        with self.canvas:
            Color(.9, .9, .9)

            for idx in range(len(self.datas)):
                x = self.center_x + rayon*cos(angle*idx)
                y = self.center_y + rayon*sin(angle*idx)
                Line(points=[self.center_x, self.center_y, x, y], width=1.0)

            Color(0, 1., 0)
            Line(points=list(itertools.chain.from_iterable(
                [(self.center_x + rayon*val * cos(angle*idx),
                  self.center_y + rayon*val * sin(angle*idx))
                 for idx, val in enumerate(self.datas)])), width=1.0, close=True)
            Color(0, 1., 0, 0.5)
            Mesh(vertices=list(itertools.chain.from_iterable(
                [(self.center_x + rayon*val * cos(angle*idx),
                  self.center_y + rayon*val * sin(angle*idx),0,0)
                 for idx, val in enumerate(self.datas)])),
                 indices=range(len(self.datas)),
                 mode='triangle_fan')


            print(list(itertools.chain.from_iterable(
                 [(self.center_x + rayon*val * cos(angle*idx),
                   self.center_y + rayon*val * sin(angle*idx))
                  for idx, val in enumerate(self.datas)])))


class TestRadarGraphApp(App):
    def build(self):
        return RadarGraph()

if __name__ == '__main__':
    TestRadarGraphApp().run()