human
I wrote the below code

    if (r_blur is None):
        r_blur = ((2 * r_zone) / 3)
    def fl(gf, t):
        im = gf(t)
        (h, w, d) = im.shape
        (x, y) = (int(fx(t)), int(fy(t)))
        (x1, x2) = (max(0, (x - r_zone)), min((x + r_zone), w))
        (y1, y2) = (max(0, (y - r_zone)), min((y + r_zone), h))
        region_size = ((y2 - y1), (x2 - x1))
        mask = np.zeros(region_size).astype('uint8')
        cv2.circle(mask, (r_zone, r_zone), r_zone, 255, (-1), lineType=cv2.CV_AA)
        mask = np.dstack((3 * [((1.0 / 255) * mask)]))
        orig = im[y1:y2, x1:x2]
        blurred = cv2.blur(orig, (r_blur, r_blur))
        im[y1:y2, x1:x2] = ((mask * blurred) + ((1 - mask) * orig))
        return im
    return clip.fl(fl)

What's a good function header?
assistant
#Here's a good function header.

def headblur(clip, fx, fy, r_zone, r_blur=None):