pygame starter example: moving a circle, changing the colors

pygame003.py

# Example file showing a circle moving on screen
import pygame

# pygame setup
pygame.init()
screen = pygame.display.set_mode((1280, 720))
clock = pygame.time.Clock()
running = True
dt = 0

player_pos = pygame.Vector2(screen.get_width() / 2, screen.get_height() / 2)
r,g,b = 255,0,0
radius = 40
while running:
    # poll for events
    # pygame.QUIT event means the user clicked X to close your window
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # fill the screen with a color to wipe away anything from last frame
    #screen.fill("purple")

    pygame.draw.circle(screen, ((r,g,b)), player_pos, radius)

    keys = pygame.key.get_pressed()
    if keys[pygame.K_w]:
        player_pos.y -= 300 * dt
    if keys[pygame.K_s]:
        player_pos.y += 300 * dt
    if keys[pygame.K_a]:
        player_pos.x -= 300 * dt
    if keys[pygame.K_d]:
        player_pos.x += 300 * dt
    if keys[pygame.K_u]:
        r += 1
        r = min(255,r)
    if keys[pygame.K_j]:
        r -= 1
        r = max(0, r)
    if keys[pygame.K_i]:
        g += 1
        g = min(255,g)
    if keys[pygame.K_k]:
        g -= 1
        g = max(0, g)
    if keys[pygame.K_o]:
        b += 1
        b = min(255,b)
    if keys[pygame.K_l]:
        b -= 1
        b = max(0, b)
    if keys[pygame.K_n]:
        radius -= 10 * dt
        radius = max(0, radius)
    if keys[pygame.K_m]:
        radius += 10 * dt
        radius = min(500, radius)
    
    # flip() the display to put your work on screen
    pygame.display.flip()
    pygame.display.set_caption(f"red {r} green {g} blue {b} radius {radius:.2f}")

    # limits FPS to 60
    # dt is delta time in seconds since last frame, used for framerate-
    # independent physics.
    dt = clock.tick(60) / 1000

pygame.quit()