алгоритм Брезенхема для окружности

def circle(start_x, start_y, radius):
    sleep(2)
    x1 = 0
    y1 = radius
    delta = 1-2*radius
    error = 0
    while y1 >= 0:
        mouseDown(button = 'left', x = start_x + x1, y = start_y + y1)
        mouseDown(button = 'left', x = start_x + x1, y = start_y - y1)
        mouseDown(button = 'left', x = start_x - x1, y = start_y + y1)
        mouseDown(button = 'left', x = start_x - x1, y = start_y - y1)
        if delta < 0 & error <=0:
            x1 +=1
            delta +=2*x1+1
        error = 2*(delta-x1)-1
        if delta > 0 & error > 0:
            y1 -=1
            delta +=1-2*y1
        x1 +=1
        delta +=2*(x1-y1)
        y1 -=1