import Image

### SETTINGS
####################
X = 800
Y = 600
BLOCK_SIZE = 20
ALTERNATE_LINES = True
COLOUR = (51, 153, 255)
BACKGROUND = (255, 255, 204)

### CONSTANTS
####################
size = X, Y
im = Image.new('RGB', size, BACKGROUND)
counter = 1

for i in range(0, (X / BLOCK_SIZE)):
    for j in range(0, (Y / BLOCK_SIZE)):
        if (i % 2) == (counter % 2):
            for x in range((i * BLOCK_SIZE), ((i * BLOCK_SIZE) + BLOCK_SIZE)):
                for y in range((j * BLOCK_SIZE), ((j * BLOCK_SIZE) + BLOCK_SIZE)):
                    im.im.putpixel((x, y), COLOUR)
        if (j % 2) == (counter % 2):
            for x in range((i * BLOCK_SIZE), ((i * BLOCK_SIZE) + BLOCK_SIZE)):
                for y in range((j * BLOCK_SIZE), ((j * BLOCK_SIZE) + BLOCK_SIZE)):
                    im.im.putpixel((x, y), COLOUR)
    if ALTERNATE_LINES:
        counter += 1
im.save('output.png')