python - How to call a function from a class from another class in kivy Pong ball game -

i'm practicing kivy ponggame code given in tutorial. want know how call function - serve_ball2() in class ponggame newly created class - pongsample. in below code created class pongsample serve second ball once first ball collide paddle.

update : can call serve_ball2() pongsample serve_ball2() doesn't function intended i.e doesn't serve ball.

i've shared complete code below. in advance

pong.py:

from kivy.app import app kivy.uix.widget import widget kivy.properties import numericproperty, referencelistproperty,\     objectproperty kivy.vector import vector kivy.clock import clock, time threading import thread  class pongpaddle(widget):     score = numericproperty(0)      def bounce_ball(self, ball):         if self.collide_widget(ball):             vx, vy = ball.velocity             offset = (ball.center_y - self.center_y) / (self.height / 2)             bounced = vector(-1 * vx, vy)             vel = bounced * 1.1             ball.velocity = vel.x, vel.y + offset             pongsample().call_game()  class pongball(widget):     velocity_x = numericproperty(0)     velocity_y = numericproperty(0)     velocity = referencelistproperty(velocity_x, velocity_y)      def move(self):         self.pos = vector(*self.velocity) + self.pos  class pongsample(widget):     def call_game(self):         print 'pongsample'         ponggame=ponggame()         ponggame.serve_ball2()  class ponggame(widget):     ball = objectproperty(none)     ball2 = objectproperty(none)     player1 = objectproperty(none)     player2 = objectproperty(none)      def serve_ball(self, vel=(4, 0)):         self.ball.center = self.center         self.ball.velocity = vel      def serve_ball2(self, vel=(3, 0)):           print 'serve_ball2'         self.ball2.center = self.center         self.ball2.velocity = vel      def serve_down(self):         print 'inside serve down'         self.ball.center = self.center         self.ball.velocity = vector(4,0).rotate(-90)      def update(self, dt):         self.ball.move()         self.ball2.move()          #bounce of paddles         self.player1.bounce_ball(self.ball)         self.player2.bounce_ball(self.ball)          #bounce ball off bottom or top         if (self.ball.y < self.y) or (self.ball.top > self.top):             self.ball.velocity_y *= -1         if (self.ball2.y < self.y) or (self.ball2.top > self.top):             self.ball2.velocity_y *= -1          #went of side score point?         if self.ball.x < self.x:             self.player2.score += 1             self.serve_ball(vel=(4, 0))         if self.ball.x > self.width:             self.player1.score += 1             self.serve_ball(vel=(-4, 0))          if self.ball2.x < self.x:             self.player2.score += 1             self.serve_ball2(vel=(3, 0))         if self.ball2.x > self.width:             self.player1.score += 1             self.serve_ball2(vel=(-3, 0))      def on_touch_move(self, touch):         if touch.x < self.width / 3:             self.player1.center_y = touch.y         if touch.x > self.width - self.width / 3:             self.player2.center_y = touch.y  class pongapp(app):     def build(self):         game = ponggame()         game.serve_ball()         clock.schedule_interval(game.update, 1.0 / 60.0)         return game  if __name__ == '__main__':     pongapp().run() 

pong.kv:

    #:kivy 1.8.0  <pongball>:     size: 50, 50      canvas:         ellipse:             pos: self.pos             size: self.size            <pongpaddle>:     size: 25, 200     canvas:         rectangle:             pos:self.pos             size:self.size  <ponggame>:     ball: pong_ball     ball2: pong_ball2     player1: player_left     player2: player_right      canvas:         rectangle:             pos: self.center_x-5, 0             size: 10, self.height      label:         font_size: 70           center_x: root.width / 4         top: root.top - 50         text: str(root.player1.score)      label:         font_size: 70           center_x: root.width * 3 / 4         top: root.top - 50         text: str(root.player2.score)      pongball:         id: pong_ball         center: self.parent.center      pongball:         id: pong_ball2         center: self.parent.center      pongpaddle:         id: player_left         x: root.x         center_y: root.center_y      pongpaddle:         id: player_right         x: root.width-self.width         center_y: root.center_y 

to use class add game.serve_ball2() to pongapp

class pongapp(app):     def build(self):         game = ponggame()         game.serve_ball()         game.serve_ball2()         clock.schedule_interval(game.update, 1.0 / 60.0)         return game 

and add self.ball2 bounce off paddles:

#bounce of paddles self.player1.bounce_ball(self.ball) self.player2.bounce_ball(self.ball) self.player1.bounce_ball(self.ball2) self.player2.bounce_ball(self.ball2)