A simple script demonstrating animation in pygame

animation.py

import pygame, sys
from pygame.locals import *

pygame.init()

FPS = 60
fpsClock = pygame.time.Clock()

DISPLAYSURF = pygame.display.set_mode((400,300), 0, 32)
pygame.display.set_caption('Animation')

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
box = pygame.Rect((10,10), (50,50))
direction = 'right'

while True:
    DISPLAYSURF.fill(BLACK)

    if direction == 'right':
        box.left += 5
        if box.left == 340:
            direction = 'down'
    elif direction == 'down':
        box.top += 5
        if box.top == 240:
            direction = 'left'
    elif direction == 'left':
        box.left -= 5
        if box.left == 10:
            direction = 'up'
    elif direction == 'up':
        box.top -= 5
        if box.top == 10:
            direction = 'right'

    pygame.draw.rect(DISPLAYSURF, WHITE, box)

    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()

    pygame.display.update()
    fpsClock.tick(FPS)