main.py

#!/usr/bin/env python2.7
# -*- coding: utf-8 -*-

import pygame
from pygame.locals import *
import sys
from sprite_anim import *

pygame.init()

display = 800, 600
FPS = 60
frames = FPS / 10

main_surface = pygame.display.set_mode(display, DOUBLEBUF)

strips = [
    SpriteStripAnim("plane_sheet.png", (0, 0, 88, 73), 3, 1, True, frames),
    SpriteStripAnim("plane_sheet.png", (88, 0, 88, 73), 3, 1, True, frames),
    SpriteStripAnim("plane_sheet.png", (176, 0, 88, 73), 3, 1, True, frames)
]

black = Color('black')
clock = pygame.time.Clock()
n = 0
strips[n].iter()
image = strips[n].next()

while True:
    for event in pygame.event.get():
        if event.type == KEYUP:
            if event.key == K_ESCAPE:
                sys.exit()
            elif event.key == K_RETURN:
                n += 1
                if n >= len(strips):
                    n = 0
                strips[n].iter()

    main_surface.fill((0, 0, 0))

    main_surface.blit(image, (0, 0))
    pygame.display.flip()
    image = strips[n].next()
    clock.tick(FPS)

sprite_anim.py

class Spritesheet(object):
    def __init__(self, filename):
        try:
            self.sheet = pygame.image.load(filename).convert_alpha()
        except pygame.error, message:
            print 'Unable to load spritesheet image:', filename
            raise SystemExit

    def image_at(self, rectangle, colorkey=None):
        """Loads image from x,y,x+offset,y+offset"""
        rect = pygame.Rect(rectangle)
        image = pygame.Surface(rect.size).convert()
        image.blit(self.sheet, (0, 0), rect)
        if colorkey is not None:
            if colorkey is -1:
                colorkey = image.get_at((0, 0))
            image.set_colorkey(colorkey, pygame.RLEACCEL)
        return image

    def images_at(self, rects, colorkey=None):
        """Loads multiple images, supply a list of coordinates"""
        return [self.image_at(rect, colorkey) for rect in rects]

    def load_strip(self, rect, image_count, colorkey=None):
        """Loads a strip of images and returns them as a list"""
        tups = [(rect[0] + rect[2] * x, rect[1], rect[2], rect[3])
                for x in range(image_count)]
        return self.images_at(tups, colorkey)


class SpriteStripAnim(object):
    """sprite strip animator

    This class provides an iterator (iter() and next() methods), and a
    __add__() method for joining strips which comes in handy when a
    strip wraps to the next row.
    """

    def __init__(self, filename, rect, count, colorkey=None, loop=False, frames=1):
        """construct a SpriteStripAnim

        filename, rect, count, and colorkey are the same arguments used
        by spritesheet.load_strip.

        loop is a boolean that, when True, causes the next() method to
        loop. If False, the terminal case raises StopIteration.

        frames is the number of ticks to return the same image before
        the iterator advances to the next image.
        """
        self.filename = filename
        ss = Spritesheet(filename)
        self.images = ss.load_strip(rect, count, colorkey)
        self.i = 0
        self.loop = loop
        self.frames = frames
        self.f = frames

    def iter(self):
        self.i = 0
        self.f = self.frames
        return self

    def next(self):
        if self.i >= len(self.images):
            if not self.loop:
                raise StopIteration
            else:
                self.i = 0
        image = self.images[self.i]
        self.f -= 1
        if self.f == 0:
            self.i += 1
            self.f = self.frames
        return image

    def __add__(self, ss):
        self.images.extend(ss.images)
        return self