Python turtle library error relating to variable which doesn't seem to have any problems

Question

I'm following a tutorial for making pong in the turtle API & for some reason I'm getting an error which seems to stop "paddle_a" from colliding. It errors out every time I close the window. The paddle a collision detection seems identical to the paddle b collision detection other than numbers being tweaked.

I'm not that great at debugging but I know it's at line 69 and it seems to affect just the collision detection with the ball of paddle_a but not the nearly identical code of paddle_b.

Traceback (most recent call last): File "c:\Users\harba\OneDrive\Desktop\New folder\Personal Projects\Games\Pong.py", line 69, in ball.setx(ball.xcor() + ball_dx) File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 1809, in setx self._goto(Vec2D(x, self._position[1])) File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 3160, in _goto screen._pointlist(self.currentLineItem), File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 754, in _pointlist File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 1809, in setx self._goto(Vec2D(x, self._position[1])) File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 3160, in _goto screen._pointlist(self.currentLineItem), File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\turtle.py", line 754, in pointlist cl = self.cv.coords(item) File "", line 1, in coords File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.10_3.10.1520.0_x64__qbz5n2kfra8p0\lib\tkinter_init.py", line 2795, in coords_tkinter.TclError: invalid command name ".!canvas"

import turtle

window = turtle.Screen()
window.title("Pong but cool")
window.bgcolor("black")
window.setup(width=800,height=600)
window.tracer(0)

#Padles
paddle_a = turtle.Turtle()
paddle_a.speed(0) 
paddle_a.shape("square")
paddle_a.color("white")
paddle_a.shapesize(stretch_wid=5, stretch_len=1)
paddle_a.penup()
paddle_a.goto(-350, 0)

paddle_b = turtle.Turtle()
paddle_b.speed(0) 
paddle_b.shape("square")
paddle_b.color("white")
paddle_b.shapesize(stretch_wid=5, stretch_len=1)
paddle_b.penup()
paddle_b.goto(350, 0)

#Ball
ball = turtle.Turtle()
ball.speed(0) 
ball.shape("square")
ball.color("white")
ball.penup()
ball.goto(0, 0)
ball.dx = 0.05
ball.dy = 0.05

#kooky Functions
def paddle_a_up():
    y = paddle_a.ycor()
    y += 20
    paddle_a.sety(y)

def paddle_a_down():
    y = paddle_a.ycor()
    y -= 20
    paddle_a.sety(y)

def paddle_b_up():
    y = paddle_b.ycor()
    y += 20
    paddle_b.sety(y)

def paddle_b_down():
    y = paddle_b.ycor()
    y -= 20
    paddle_b.sety(y)


#keyboard binding
window.listen()
window.onkeypress(paddle_a_up, "w")
window.onkeypress(paddle_a_down, "s")
window.onkeypress(paddle_b_up, "Up")
window.onkeypress(paddle_b_down, "Down")

while True:
    window.update()

    #balls
    ball.setx(ball.xcor() + ball.dx)
    ball.sety(ball.ycor() + ball.dy)

    #border checking
    if ball.ycor() > 290:
        ball.sety(290)
        ball.dy *= -1
    if ball.ycor() < -290:
        ball.sety(-290)
        ball.dy *= -1
        
    if ball.xcor() > 390:
        ball.goto(0, 0)
        ball.dx *= -1
    if ball.xcor() < -390:
        ball.goto(0, 0)
        ball.dx *= -1
    
    #collisions
    if (ball.xcor() > 340 and ball.xcor() < 350) and (ball.ycor() < paddle_b.ycor() + 50 and ball.ycor() > paddle_b.ycor() - 50):
        ball.setx(340)
        ball.dx *= -1
    if (ball.xcor() > -340 and ball.xcor() < -350) and (ball.ycor() < paddle_a.ycor() + 50 and ball.ycor() > paddle_a.ycor() - 50):
        ball.setx(-340)
        ball.dx *= -1

The final if statement inside the game loop doesn't seem to work & in the balls section is where the error seems to originate.

Answer 1

This can never be true:

ball.xcor() > -340 and ball.xcor() < -350

You have to reverse your geometric thinking when working with negative coordinates:

-340 > ball.xcor() > -350

My rework of your code:

from turtle import Screen, Turtle

def paddle_a_up():
    paddle_a.sety(paddle_a.ycor() + 20)

def paddle_a_down():
    paddle_a.sety(paddle_a.ycor() - 20)

def paddle_b_up():
    paddle_b.sety(paddle_b.ycor() + 20)

def paddle_b_down():
    paddle_b.sety(paddle_b.ycor() - 20)

def play():
    x, y = ball.position()
    ball.setposition(x + ball.dx, y + ball.dy)

    # border checking
    if ball.ycor() > 290:
        ball.sety(290)
        ball.dy *= -1
    elif ball.ycor() < -290:
        ball.sety(-290)
        ball.dy *= -1

    if ball.xcor() > 390:
        ball.goto(0, 0)
        ball.dx *= -1
    elif ball.xcor() < -390:
        ball.goto(0, 0)
        ball.dx *= -1

    # collisions
    if 340 < ball.xcor() < 350 and paddle_b.ycor() - 50 < ball.ycor() < paddle_b.ycor() + 50:
        ball.setx(340)
        ball.dx *= -1
    elif -340 > ball.xcor() > -350 and paddle_a.ycor() - 50 < ball.ycor() < paddle_a.ycor() + 50:
        ball.setx(-340)
        ball.dx *= -1

    screen.update()
    screen.ontimer(play, 10)

screen = Screen()
screen.title("Pong but cool")
screen.bgcolor('black')
screen.setup(width=800, height=600)
screen.tracer(0)

# Padles
paddle_a = Turtle()
paddle_a.shape('square')
paddle_a.color('white')
paddle_a.shapesize(stretch_wid=5, stretch_len=1)
paddle_a.penup()
paddle_a.setx(-350)

paddle_b = paddle_a.clone()
paddle_b.setx(350)

# Ball
ball = Turtle()
ball.shape('square')
ball.color('white')
ball.penup()

ball.dx = 2.0  # user-defined properties
ball.dy = 2.0

# keyboard binding
screen.onkeypress(paddle_a_up, 'w')
screen.onkeypress(paddle_a_down, 's')
screen.onkeypress(paddle_b_up, 'Up')
screen.onkeypress(paddle_b_down, 'Down')
screen.listen()

play()

screen.mainloop()