巡线代码，我的代码按照巡线小车实验改的，为什么老是报错？

p4mo

THRESHOLD = (8, 40, -18, 0, -3, 19)
import sensor, image, time
from pyb import UART
from pid import PID
import ustruct
rho_pid = PID(p=0.17, i=0)
theta_pid = PID(p=0.001, i=0)
sensor.reset()
sensor.set_vflip(True)
sensor.set_hmirror(True)
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QQQVGA)
sensor.skip_frames(time = 2000)
clock = time.clock()
uart = UART(3, 115200)
output=0

while(True):
    clock.tick()
    img = sensor.snapshot().binary([THRESHOLD])
    line = img.get_regression([(100,100)], robust = True)
    if (line):
        rho_err = abs(line.rho())-img.width()/2
        if line.theta()>90:
            theta_err = line.theta()-180
        else:
            theta_err = line.theta()
        img.draw_line(line.line(), color = 127)
        print(rho_err,line.magnitude(),rho_err)
        if line.magnitude()>8:
            #if -40<b_err<40 and -30<t_err<30:
            rho_output = rho_pid.get_pid(rho_err,1)
            theta_output = theta_pid.get_pid(theta_err,1)
            output = rho_output+theta_output
        else:
           output=0.0 
    else:
       output=0.0 
       pass
    date=bytearray([0x2C,0x12,int(output),0x00,0x00,0x00,0x5B])
	uart.write(date)