为什么矩形对象只能用for语句创建，不可以直接用=创建？

[syxh]

THRESHOLD =(23, 103)
import sensor, image
from pyb import LED,Timer,Pin

sensor.reset()
sensor.set_vflip(True)
sensor.set_hmirror(True)
sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_framesize(sensor.QQQVGA)
sensor.set_auto_whitebal(True)
sensor.skip_frames(time = 2000)
clock = time.clock()

while(True):
    clock.tick()
    img = sensor.snapshot().mean(3).binary([THRESHOLD])
    img.draw_rectangle((0,10,80,60))
    rec = img.find_rects(roi=(0,20,80,60),threshold=55000)
    img.draw_rectangle(rec.rect(), color = (0, 255, 0))
    '''for rec in img.find_rects(roi=(0,20,80,60),threshold=55000):
        img.draw_rectangle(rec.rect(), color = (0, 255, 0))'''

[kidswong999]

img.find_rects返回的是列表，多个矩形，而不是一个矩形。