pkengine.py

import pygame

class EngineObject:
    def __init__(self):
        self.children=[]
        self.running=False
    def prepare(self):pass
    def finalize(self):pass
    def pre_frame(self):pass
    def post_frame(self):pass
    def __iter__(self):
        print(type(self).__name__,"Beginning iteration.")
        if not self.running:
            self.prepare()
            self.running=True
        return self
    def __next__(self):
        self.pre_frame()
        for child in self.children[:]:
            try:
                next(child)
            except StopIteration:
                self.children.remove(child)
        self.post_frame()
        if not self.running:
            self.finalize()
            raise StopIteration

class GameObject(EngineObject):
    def __init__(self, engine):
        EngineObject.__init__(self)
        self.engine = engine

class Timer(EngineObject):
    def __init__(self,dur,repeat=False):
        self.duration, self.elapse = dur, 0
        self.repeat = repeat
        self.timer = pygame.time.Clock()
    def pre_frame(self):
        self.elapse += self.timer.tick()
    def post_frame(self):
        if self.elapse >= self.duration:
            self.elapse()
            if self.repeat:
                self.elapse = self.elapse % self.duration
            else:
                self.running = False
    def elapse(self):pass

class Intro(GameObject):
    class FadeTimer(Timer):
        def __init__(self):Timer.__init__(self, 200, True)
        def prepare(self):self.color = 0
        def elapse(self):self.color = self.color + 1 % 256
    def prepare(self):
        #Load any images, fonts, etc.
        print("INTRO.PREPARE")
        self.timer = self.Timer()
    def pre_frame(self):
        self.engine.window.fill([self.timer.color]*3)

class PKEngine(EngineObject):
    frame_rate = 30#30 fps should be good, no?
    resolution = (320, 240)
    def __init__(self):
        EngineObject.__init__(self)
        self.frame_limiter = pygame.time.Clock()

    def prepare(self):
        print("PKENGINE.PREPARE")
        pygame.display.init()
        self.window = pygame.display.set_mode(self.resolution)
        self.children.append(Intro(self))

    def finalize(self):
        pygame.quit()

    def post_frame(self):
        self.window.update()
        self.frame_limiter(self.frame_rate)
        if len(self.children)<1:
            self.running = False

engine = PKEngine()
for frame in engine:pass