My Pygame Scene Handler.

# Still working on this.
import pygame.display
from pygame.time import Clock

class Scene:
    def __init__(self, control):
        self.control = control

    def on_focus_gain(self): pass
    def on_focus_lost(self): pass

    def on_draw(self, surface): pass
    def on_event(self, event): pass
    def on_update(self, delta): pass

    # Interface, Control Display Handler
    def clear_stack(self):
        self.control.handler.stack_clear()

    def pop_scene(self):
        self.control.handler.stack_pop()

    def push_scene(self):
        self.control.handler.stack_push()

    def set_scene(self, scene):
        self.control.handler.set_scene(scene)

    def on_quit(self):
        self.control.quit()

class SceneHandler:
    def __init__(self):
        self.current_scene = None
        self.next_scene = None
        self.scenes = {}
        self.stack = []

    def set_scene(self, scene):
        if isinstance(scene, Scene):
            push_scene = scene
        else:
            push_scene = self.scenes[scene]

        if push_scene:
            if self.current_scene is None:
                self.current_scene = push_scene
            else:
                self.next_scene = push_scene

    def stack_clear(self):
        self.stack = []

    def stack_empty(self):
        return len(self.stack == 0)

    def stack_pop(self):
        if len(self.stack) > 0:
            self.next_scene = self.stack[-1]
            self.stack = self.stack[:-1]

    def stack_push(self):
        if self.current_scene:
            self.stack.append(self.current_scene)

    def update(self):
        if self.next_scene:
            if self.current_scene:
                self.current_scene.on_focus_lost()

            self.current_scene = self.next_scene
            self.current_scene.on_focus_gain()
            self.next_scene = None

        return self.current_scene

class Display:
    def __init__(self, caption, width, height, flags=0, fps=60):
        pygame.display.set_caption(caption)
        self.display = pygame.display.set_mode((width, height), flags)
        self.rect = self.display.get_rect()
        self.clock = Clock()
        self.running = True
        self.delta = 0
        self.fps = fps

        self.handler = SceneHandler()

    def loop(self):
        while (self.running):
            scene = self.handler.update()
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    scene.on_quit()
                else:
                    scene.on_event(event)

            scene.on_update(self.delta)
            scene.on_draw(self.display)
            pygame.display.flip()
            self.delta = self.clock.tick(self.fps) / 1000

class SceneControl:
    def __init__(self, caption, width, height, flags=0, fps=60):
        self.display = Display(caption, width, height, flags, fps)
        self.handler = self.display.handler

    def add_scene(self, key, scene):
        self.handler.scenes[key] = scene

    def run(self, scene=None):
        if scene is None:
            scene = Scene(self)

        self.handler.set_scene(scene)
        self.display.loop()

    def quit(self):
        self.display.running = False