circle.py

import sys, random, math, pygame
from pygame.locals import *

#main program begins
pygame.init()
screen = pygame.display.set_mode((600, 500))
pygame.display.set_caption("Circle Demo")
screen.fill((0, 0, 100))
pos_x = 300
pos_y = 250
radius = 200
angle = 360

#repeating loop
while True:
	for event in pygame.event.get():
		if event.type == QUIT:
			sys.exit()
	keys = pygame.key.get_pressed()
	if keys[K_ESCAPE]:
		sys.exit()
		
	#increment angle
	angle += 1
	if angle >= 360:
		angle = 0
		r = random.randint(0, 255)
		g = random.randint(0, 255)
		b = random.randint(0, 255)
		color = r, g, b
	
	#calculate coordinates
	x = math.cos(math.radians(angle)) * radius
	y = math.sin(math.radians(angle)) * radius
	
	#draw one step around the circle
	pos = (int(pos_x + x), int(pos_y + y))
	pygame.draw.circle(screen, color, pos, 10, 0)
	pygame.display.update()