Python Image Resizer

img-resize.py

import os
import sys
from PIL import Image

def is_image(filename):
    return filename[-3:].lower() in ["png", "jpg", "jpeg", "bmp"]

def resize_images_in(folder):
    for filename in os.listdir(folder):
        if not is_image(filename):
            continue
        filepath = os.path.join(folder, filename)
        img = Image.open(filepath)
        w = 1200
        h = 1200
        large_img = img.resize((w, h), Image.ANTIALIAS)
        large_img.save(filepath)
        thumbnail = img.resize((w/4, h/4), Image.ANTIALIAS)
        thumbnail.save(folder + 'small/' + filename)

print('Resizing images...')

folder = './i/'
if not os.path.exists(folder + 'small/'):
    os.makedirs(folder + 'small/')

resize_images_in(folder);

print('...done.')