opencv 画矩形

import cv2
import numpy as np

class App:
    startX = 0
    startY = 0
    flag_rect = False
    def onmouse(self, event, x, y, flags, param):
        if event == cv2.EVENT_LBUTTONDOWN:
            self.flag_rect = True
            self.startX = x
            self.startY = y
            print('EVENT_LBUTTONDOWN',x,y)
        elif event == cv2.EVENT_LBUTTONUP:
            cv2.rectangle(self.img,
                          (self.startX,self.startY),
                          (x,y),
                          (0,0,255),
                          2
                          )
            # print('EVENT_LBUTTONUP')
            self.flag_rect = False
            pass
        elif event == cv2.EVENT_MOUSEMOVE:
            if self.flag_rect:
                self.img = self.img2.copy()
                cv2.rectangle(self.img,
                              (self.startX,self.startY),
                              (x,y),
                              (0,0,255),
                              2
                              )
            # print('EVENT_MOUSEMOVE')
            pass
    def run(self):
        print('run....')
        cv2.namedWindow('input')
        cv2.setMouseCallback('input',self.onmouse)
        self.img = cv2.imread('imgs/lena.png')
        self.img2 = self.img.copy()
        while(1):
            cv2.imshow('input',self.img)
            k = cv2.waitKey(100)
            if k == 27:
                break
App().run()