Python - Turtle - Pong - (Stackoverflow)

#!/usr/bin/env python3

"""
# date: 2024.06.28
# [Second instance of a class suppresses/deletes the first one in my Python program - Stack Overflow](https://stackoverflow.com/questions/78677249/second-instance-of-a-class-suppresses-deletes-the-first-one-in-my-python-program?noredirect=1#comment138718516_78677249)
"""

from turtle import Turtle
from turtle import Screen

# --- constants ---  # PEP8: `UPPER_CASE_NAMES`

# BOX = 30

# --- classes ---

class Paddle:

    def __init__(self, side, key_left, key_right, x, color):

        self.key_left = key_left
        self.key_right = key_right

        self.paddle = Turtle(shape="square")
        self.paddle.color(color)
        self.paddle.penup()
        self.paddle.setx(x)
        self.paddle.sety(0)

        self.pressed_up = False
        self.pressed_down = False

        self.paddle.screen.onkeypress(key=self.key_left,  fun=self.move_up)
        self.paddle.screen.onkeypress(key=self.key_right, fun=self.move_down)

        self.paddle.screen.onkeyrelease(key=self.key_left,  fun=self.move_up_stop)
        self.paddle.screen.onkeyrelease(key=self.key_right, fun=self.move_down_stop)

        half_height = screen.canvheight // 2

        self.range_top    =  half_height - 10
        self.range_bottom = -half_height + 10
        #print('[DEBUG]', self.range_top, self.range_bottom)

        self.speed = 0

    def update(self):

        if self.pressed_up and self.pressed_down:  # both keys are presse then don't move
            self.speed = 0
        elif self.pressed_up:    # only one is pressed
            self.speed = 5
        elif self.pressed_down:  # only one is pressed
            self.speed = -5
        else:  # both keys are unpressed
            self.speed = 0

        if self.speed != 0:
            current_y = self.paddle.ycor()
            new_y = current_y + self.speed

            if self.range_top > new_y > self.range_bottom:
                self.paddle.sety(new_y)

    # I don't do calculation here (and don't execute `update()`
    # because key repeates presses slow and it slows all movement
    def move_up(self):
        self.pressed_up = True

    def move_down(self):
        self.pressed_down = True

    def move_up_stop(self):
        self.pressed_up = False

    def move_down_stop(self):
        self.pressed_down = False

class Ball:

    def __init__(self, x=0, y=0, color='black'):
        self.ball = Turtle(shape="square")
        self.ball.color(color)
        self.ball.penup()
        self.ball.setx(x)
        self.ball.sety(y)
        self.speed_x = 3
        self.speed_y = 3

        half_width = screen.canvwidth // 2
        half_height = screen.canvheight // 2

        self.range_top    =  half_height - 10
        self.range_bottom = -half_height + 10
        self.range_left   =  half_width - 10
        self.range_right  = -half_width + 10

    def update(self):
        current_x = self.ball.xcor()
        current_y = self.ball.ycor()
        new_x = current_x + self.speed_x
        new_y = current_y + self.speed_y

        if new_x < self.range_right or new_x > self.range_left:
            self.speed_x = -self.speed_x
        if new_y > self.range_top   or new_y < self.range_bottom:
            self.speed_y = -self.speed_y

        self.ball.setx(new_x)
        self.ball.sety(new_y)

# --- functions ----

def mainloop():
    left_pad.update()
    right_pad.update()
    ball.update()

    screen.update()

    # update after ? ms
    screen.ontimer(mainloop, 5)

# --- main ---

screen = Screen()
screen.bgcolor("beige")
screen.title("Pong!")
screen.setup(width=820, height=620)
screen.screensize(canvwidth=800, canvheight=600)
screen.tracer(0)
screen.listen()

half_width = screen.canvwidth // 2

x = -half_width + 20
left_pad  = Paddle("left", "w", "s", x, 'red')

x =  half_width - 20
right_pad = Paddle("right", "Up", "Down", x, 'green')

ball = Ball()

mainloop()

screen.exitonclick()