add function to cancel game

games/pong.py

@@ -183,6 +183,8 @@ class Playground(object):
         paddleRight = Paddle(self, width - 1, (height - paddlesize)//2, paddlesize)
         self.__paddles = [paddleLeft, paddleRight]
 
+        self.cancelled = False
+
         self.__ball = Ball(self, 0, 0, 1, 1)
         self.__gameTickCallbacks = []
         self.__newRoundCallbacks = []
@@ -227,6 +229,9 @@ class Playground(object):
                 if paddle.containsPoint(x, y):
                     return paddle
 
+    def cancel(self):
+        self.cancelled = True
+
     def play(self, serve=None):
         leftPaddle = self.__paddles[0]
         rightPaddle = self.__paddles[1]
@@ -250,7 +255,7 @@ class Playground(object):
             callback()
 
         ticks = 0
-        while True:
+        while not self.cancelled:
             ticks += 1
             time.sleep(0.08)
             if ticks %2 == 0: