How do I make this pymunk code work? It shows a black screen

I am new to stackoverflow.
My code has a problem which the screen turns completely black.
The error.
I need the answer quickly so any help will be good.
Heres the code:

import pygame, sys
import pymunk
import pymunk.pygame_util
from pymunk.vec2d import Vec2d
size = (800, 800)
FPS = 120

space = pymunk.Space()
space.gravity = (0,250)

pygame.init()
screen = pygame.display.set_mode(size)
clock = pygame.time.Clock()

class Ball:
    global space
    def __init__(self, pos):
        self.body = pymunk.Body(1,1, body_type = pymunk.Body.DYNAMIC)
        self.body.position = pos
        self.radius = 60
        self.shape = pymunk.Circle(self.body, self.radius)

        space.add(self.body, self.shape)
        def draw(self):
            x = int(self.body.position.x)
            y = int(self.body.position.y)
            pygame.draw.circle(screen, (255,0,0), (x,y), self.radius)

balls = []
balls.append(Ball((400,0)))
balls.append(Ball((100,0)))
balls.append(Ball((600,100)))

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

            screeen.fill(217,217,217)

            for ball in balls:
                ball.draw()

            space.step(1/50)
            pygame.display.update()
            clock.tick(FPS)

Any help on what to do???
Thanks.

>Solution :

1. screeen.fill(217,217,217) should be screen.fill((217,217,217))

2. The Indentation is not correct. In particular, the scene must be pulled in the application loop and not in the bleed loop:

import pygame, sys
import pymunk
import pymunk.pygame_util
from pymunk.vec2d import Vec2d
size = (800, 800)
FPS = 120

space = pymunk.Space()
space.gravity = (0,250)

pygame.init()
screen = pygame.display.set_mode(size)
clock = pygame.time.Clock()

class Ball:
    global space
    def __init__(self, pos):
        self.body = pymunk.Body(1,1, body_type = pymunk.Body.DYNAMIC)
        self.body.position = pos
        self.radius = 60
        self.shape = pymunk.Circle(self.body, self.radius)

        space.add(self.body, self.shape)

    # INDENTATION
    #<--|

    def draw(self):
        x = int(self.body.position.x)
        y = int(self.body.position.y)
        pygame.draw.circle(screen, (255,0,0), (x,y), self.radius)

balls = []
balls.append(Ball((400,0)))
balls.append(Ball((100,0)))
balls.append(Ball((600,100)))

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    # INDENTATION
    #<------|    

    screen.fill((217,217,217))

    for ball in balls:
        ball.draw()

    space.step(1/50)
    pygame.display.update()
    clock.tick(FPS)