Blank gif created from .png files by images2gif.py

Question

I'm trying to create a gif from pygame's frames saved using pygame.image.save, lets say that frames are already saved in runtime directory and then I use this code:

file_names = sorted((fn for fn in os.listdir('.') if fn.endswith('.png')))

images = [Image.open(fn) for fn in file_names]

filename = "my_gif.GIF"
writeGif(filename, images, duration=1.0, dither=0)

there is no error after running that and .gif file weights 21 KB but everything I can see is black screen (even though .png files don't have anything in black color).

However previously there was an error in images2gif.py:

fp.write(globalPalette)
TypeError: must be string or buffer, not None

and I fixed that using method from the best answer in this question: Error in images2gif.py with GlobalPalette

and now it doesn't raise any errors but .gif file is entirely black.

I use Python 2.7.6

Here is a full code to generate .png and then .gif:

import pygame, sys, os
from images2gif import writeGif as writeGif
from PIL import Image
from pygame.locals import *

def main():
    pygame.init()
    surface = pygame.display.set_mode((800, 600), 0, 32)
    surface.fill((255,0,0))

    center = (800 // 2, 600 // 2)

    count = 1
    while (count < 26):
        for event in pygame.event.get():
            if event.type==QUIT:
                pygame.quit()
                sys.exit()
        pygame.draw.rect(surface, (0, 255, 255), (center[0], center[1] + (count * 5), 5, 5))
        filename = 'frame-%03d.png' % (count)
        count = count + 1
        pygame.image.save(surface, filename)

    pygame.quit()

    file_names = sorted((fn for fn in os.listdir('.') if fn.endswith('.png')))

    images = [Image.open(fn) for fn in file_names]

    filename = "my_gif.GIF"
    writeGif(filename, images, duration=1.0, dither=0)
    sys.exit()

main()

Maybe there is a better way to create a gif or movie from these .png files? I don't have to use images2gif.py