pajton problem

import pygame, sys

pygame.init()

gamename = pygame.display.set_caption('Pong')

clock = pygame.time.Clock()
FPS = 30

black = (0, 0, 0)
white = (255, 255, 255)

screen = pygame.display.set_mode((800, 800))
screen.fill(black)

def drawline():
    pygame.draw.line(screen, white, (400, 800), (400, 0), 5)

class Ball(object):
    def __init__(self, screen):
        ballw = 26
        ballh = 26
        ballx = 387
        bally = 400
        xdist = 5
        ydist = 5
        self.ballw = ballw
        self.ballh = ballh
        self.ballx = ballx
        self.bally = bally
        self.xdist = xdist
        self.ydist = ydist
        self.screen = screen

    def draw(self):
        ball = pygame.rect.Rect((self.ballx, self.bally, self.ballw, self.ballh))
        pygame.draw.rect(screen, white, ball)

    def move(self):


    def bounce(self):


class PlayerOne(object):
    def __init__(self, screen):
        padx = 20
        pady = 350
        padh = 120
        padw = 25
        dist = 10
        self.padx = padx
        self.pady = pady
        self.padh = padh
        self.padw = padw
        self.dist = dist
        self.screen = screen

    def draw(self):
        playeronepaddle = pygame.rect.Rect((self.padx, self.pady, self.padw, self.padh))
        pygame.draw.rect(self.screen, white, playeronepaddle)

    def controlsandcollision(self):
        key = pygame.key.get_pressed()
        if key[pygame.K_w]:
            if self.pady <= 0: self.pady + 0
            else: self.pady -= self.dist
        elif key[pygame.K_s]:
            if self.pady >= 680: self.pady + 0
            else: self.pady += self.dist

class PlayerTwo(object):
    def __init__(self, screen):
        pady = 350
        padx = 760
        padh = 120
        padw = 25
        dist = 10
        self.pady = pady
        self.padx = padx
        self.padh = padh
        self.padw = padw
        self.dist = dist
        self.screen = screen

    def draw(self):
        playertwopaddle = pygame.rect.Rect((self.padx, self.pady, self.padw, self.padh))
        pygame.draw.rect(self.screen, white, playertwopaddle)

    def controlsandcollision(self):
        key = pygame.key.get_pressed()
        if key[pygame.K_UP]:
            if self.pady <= 0: self.pady + 0
            else: self.pady -= self.dist
        elif key[pygame.K_DOWN]:
            if self.pady >= 680: self.pady + 0
            else: self.pady += self.dist



pygame.display.update()

ball = Ball(screen)
playerone = PlayerOne(screen)
playertwo = PlayerTwo(screen)
ball.move()

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

    screen.fill(black)
    drawline()
    ball.draw()
    ball.move()
    playerone.controlsandcollision()
    playerone.draw()
    playertwo.controlsandcollision()
    playertwo.draw()
    pygame.display.update()
    clock.tick(FPS)