Bouncing Balls

balls.py

import sys, pygame
import random

pygame.display.init()

size = width, height = 1000, 1000
background = 0, 0, 0

screen = pygame.display.set_mode(size)
pygame.display.set_caption("Balls")

file = open('ball.txt', 'r')
lines = file.readlines()

balls = []

class Ball:
    def __init__(self):
        self.x = 0
        self.y = 0
        self.size = 0
        self.x_velocity = random.randint(0, 100) / 100
        self.y_velocity = 0
        self.force_loss = 0.0
        self.colour = (random.randint(100,255), 0, 0)

for line in lines:
    if (len(line.strip()) == 0):
        # The line is empty, skip this line.
        continue

    parts = line.split()
    if (parts[0] == "Ball"):
        # The line is a ball command, lets create a ball.
        new_ball = Ball()
        new_ball.x = int(parts[1])
        new_ball.y = int(parts[2])
        new_ball.size = int(parts[3])
        new_ball.force_loss = float(parts[4])
        
        balls.append(new_ball)

file.close()

while 1:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
    
    # Clear the screen, render the balls and display.
    screen.fill(background)

    for ball in balls:
        # Lets apply gravity to the balls.
        ball.y_velocity += 0.0005    # Gravity
        ball.y += ball.y_velocity

        ball.x += ball.x_velocity

        # Lets detect the ball hits the bottom.
        if (ball.y > 1000 - ball.size):
            ball.y = 1000 - ball.size
            ball.y_velocity = -ball.y_velocity
            ball.y_velocity *= ball.force_loss      # Lose 10% of the balls force when it bounces.

        if (ball.x > 1000 - ball.size):
            ball.x = 1000 - ball.size
            ball.x_velocity = -ball.x_velocity

        if (ball.x < 0 + ball.size):
            ball.x = 0 + ball.size
            ball.x_velocity = -ball.x_velocity

        pygame.draw.circle(screen, ball.colour, (ball.x, ball.y), ball.size)
    
    pygame.display.flip()