Fade effect for pygame

fadehandler.py

import pygame

display = None
fade_surface = None
tick = 0
speed = 10
anim_state = None
anim_func = None

def init():
    global display, fade_surface
    display = pygame.display.get_surface()
    fade_surface = pygame.Surface(display.get_size()).convert()
    fade_surface.fill((0, 0, 0))

def update():
    global tick, speed, anim_state, anim_func, display, fade_surface, fade_out

    if anim_state == "fade_in" and tick > 0:
        fade_surface.set_alpha(256 - tick)
        display.blit(fade_surface, (0, 0))

    elif anim_state == "fade_out" and tick > 0:
        fade_surface.set_alpha(tick)
        display.blit(fade_surface, (0, 0))

    elif anim_state == "fade_in2":
        fade_surface.set_alpha(256 - tick)
        display.blit(fade_surface, (0, 0))

    tick -= speed
    if tick < 0:
        tick = 0
        if anim_state:
            if anim_state == "fade_in2":
                anim_func()
                fade_out(None)

            elif anim_state == "fade_in":
                anim_func()
                anim_state = None
                anim_func = None

            elif anim_state == "fade_out" and anim_func:
                anim_func()
                anim_state = None
                anim_func = None

            else:
                anim_state = None
                anim_func = None

def fade_in(func):
    global anim_state, anim_func, tick
    tick = 256
    anim_state = "fade_in"
    anim_func = func

def fade_out(func):
    global anim_state, anim_func, tick
    tick = 256
    anim_state = "fade_out"
    anim_func = func

def fade(func):
    global anim_state, anim_func, tick
    tick = 256
    anim_state = "fade_in2"
    anim_func = func