from pygame import *

init()
window = display.set_mode((800, 600))
window.fill(Color('#ffffff'))
draw.rect(window, Color('#cccccc'), [0, 0, 100, 100])

run = 1

while run:
    for e in event.get():
        if e.type == MOUSEBUTTONDOWN:
            window.fill(Color('#ffffff'))
            position = mouse.get_pos()
            draw.rect(window, Color('#cccccc'), [position[0] - 50, position[1] - 50, 100, 100])
        if e.type == QUIT:
            run = 0

    display.update()

quit()