import turtle

wn = turtle.Screen()
wn.bgcolor("black")
wn.title("ping pong")
wn.setup(800,600)
wn.tracer(0)

Score

score_RED = 0
score_BLUE = 0

Paddle A

paddle_a = turtle.Turtle()
paddle_a.speed(0)
paddle_a.shape("square")
paddle_a.color("blue")
paddle_a.shapesize(stretch_wid=5,stretch_len=1,outline=2)
paddle_a.penup()
paddle_a.goto(-350,0)

Paddle B

paddle_b = turtle.Turtle()
paddle_b.speed(0)
paddle_b.shape("square")
paddle_b.color("red")
paddle_b.shapesize(stretch_wid=5,stretch_len=1,outline=2)
paddle_b.penup()
paddle_b.goto(350,0)

Ball

ball = turtle.Turtle()
ball.speed(0)
ball.shape("circle")
ball.color("white")
ball.penup()
ball.goto(0,0)
ball.dx = 2
ball.dy = -2

Pen

pen = turtle.Turtle()
pen.speed(0)
pen.color("white")
pen.penup()
pen.hideturtle()
pen.goto(0,260)
pen.write("BLUE : 0 RED : 0 ", align="center",font=("Courier",24,"normal"))

Function

def paddle_a_up():
y = paddle_a.ycor()
y += 20
paddle_a.sety(y)

def paddle_a_down():
y = paddle_a.ycor()
y -= 20
paddle_a.sety(y)

def paddle_b_up():
y = paddle_b.ycor()
y += 20
paddle_b.sety(y)

def paddle_b_down():
y = paddle_b.ycor()
y -= 20
paddle_b.sety(y)

Keyboard binding

wn.listen()
wn.onkeypress(paddle_a_up,"w")
wn.onkeypress(paddle_a_down,"s")
wn.onkeypress(paddle_b_up,"Up")
wn.onkeypress(paddle_b_down,"Down")

Main game loop

while True:
wn.update()

#Move the ball
ball.sety(ball.ycor()+ ball.dy)
ball.setx(ball.xcor()+ ball.dx)


#Border checking
if ball.ycor() > 290:
     ball.sety(290)
     ball.dy *= -.9

if ball.ycor() < -290:
     ball.sety(-290)
     ball.dy *= -.9


if ball.xcor() > 390:
     ball.goto(0,0)
     ball.dx*=-.9
     score_RED += 1
     pen.clear()
     pen.write("BLUE : {} RED  : {} ". format (score_RED,score_BLUE),align="center", font=("Courier", 24, "normal"))

if ball.xcor() < -390:
     ball.goto(0,0)
     ball.dx*=-.9
     score_BLUE += 1
     pen.clear()
     pen.write("BLUE : {} RED  : {} ". format (score_RED, score_BLUE), align="center", font=("Courier", 24, "normal"))

# Paddle and ball collisions
if(ball.xcor()> 340 and ball.xcor()< 350)and(ball.ycor() < paddle_b.ycor()+40 and ball.ycor()> paddle_b.ycor() -40):
    ball.setx(340)
    ball.dx *= -1

if(ball.xcor() < -340 and ball.xcor()< -350)and(ball.ycor() < paddle_a.ycor()+40 and ball.ycor()> paddle_a.ycor() -40):
    ball.setx(-340)
    ball.dx *= -1