PYTHON: bolas que reboten cuando choquen

x1 = 0

y1 = 0

dx1 = 0

dy1 = 0

x2 = 0

y2 = 0

dx2 = 0

dy2 = 0

r = 30

def setup():

    size(600, 400)

    frameRate(500)

    global x1, y1, dx1, dy1, x2, y2, dx2, dy2

    

    x1 = random(60, 500)

    y1 = random(60, 300)

    x2 = random(60, 500)

    y2 = random(60, 300)

    dx1 = random(-1, 1)

    dy1 = random(-1, 1)

    dx2 = random(-1, 1)

    dy2 = random(-1, 1)

def draw():

    global x1, y1, dx1, dy1, x2, y2, dx2, dy2

    

    background(220)

    ellipse(x1, y1, r * 2, r * 2)

    ellipse(x2, y2, r * 2, r * 2)

    x1 = x1 + dx1

    y1 = y1 + dy1

    x2 = x2 + dx2

    y2 = y2 + dy2

    if x1 - r < 0 or x1 + r > width:

        dx1 = dx1 * -1

    if y1 - r < 0 or y1 + r > height:

        dy1 = dy1 * -1

    if x2 - r < 0 or x2 + r > width:

        dx2 = dx2 * -1

    if y2 - r < 0 or y2 + r > height:

        dy2 = dy2 * -1

    

    d = dist(x1, y1, x2, y2)

    if d <= r * 2:

        tx = dx1

        ty = dy1

        dx1 = dx2

        dy1 = dy2

        dx2 = tx