fix the code moving a rect

import pygame

pygame.init()

black = [0, 0, 0]

white = [255,255,255]

red = [255, 0, 0]

rect_x = 0

sizeX = 400

sizeY = 500

#define window sizeX, sizeY in values

size = [sizeX, sizeY]

#by values

rectWidth = 50

#define width of a rect

screen = pygame.display.set_mode(size)

pygame.display.set_caption("Denkybrain Loves Graphics")

done = False

look = 0

clock = pygame.time.Clock()

while done == False:

    for event in pygame.event.get() :

        if event.type == pygame.QUIT :

            done = True

    screen.fill(white)

    if look == 0 :

        rect_x = rect_x + 0.1

        if rect_x > sizeX-rectWidth :

            look = 1

    else :

        if rect_x < 0 :

            look = 0

        rect_x = rect_x - 0.1

    pygame.draw.rect(screen, black, [rect_x,50,50,50])

    pygame.display.flip()

pygame.quit()