问函数'cvSetMouseCallback‘中的空窗口处理程序

EN

import cv2
import numpy as np

# mouse callback function
def draw_circle(event,x,y,flags,param):
    if event == cv2.EVENT_LBUTTONDBLCLK:
        cv2.circle(img,(x,y),100,(255,0,0),-1)

# Create a black image, a window and bind the function to window
img = np.zeros((512,512,3), np.uint8)
cv2.namedWindow('image')
cv2.setMouseCallback('image',draw_circle)

while(1):
    cv2.imshow('image',img)
    if cv2.waitKey(20) & 0xFF == 27:
        break
cv2.destroyAllWindows()

(most recent call last)
<ipython-input-1-640e54baca5f> in <module>
     10 img = np.zeros((512,512,3), np.uint8)
     11 cv2.namedWindow('image')
---> 12 cv2.setMouseCallback('image',draw_circle)
     13 
     14 while(1):

error: OpenCV(4.3.0) /io/opencv/modules/highgui/src/window_QT.cpp:717: error: (-27:Null pointer) NULL window handler in function 'cvSetMouseCallback'