Cannot Set Call Back to Named Window - using opencv.org example code

[Rylangrayston]

• OpenCV version 4.3.0
• Operating System / Platform => Ubuntu 20.04 64 Bit freshly installed and updated.
• python3

this code copied directly from the cv website (https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_gui/py_mouse_handling/py_mouse_handling.html#mouse-handling):

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()

Fails with this error:

Failed to load module "canberra-gtk-module"
Traceback (most recent call last):
  File "paint.py", line 12, in <module>
    cv2.setMouseCallback('image',draw_circle)
cv2.error: OpenCV(4.3.0) /io/opencv/modules/highgui/src/window_QT.cpp:717: error: (-27:Null pointer) NULL window handler in function 'cvSetMouseCallback'

[alalek]

You using Pypi opencv-python* package (unofficial) with conflicted Qt binaries.
There is nothing to fix in OpenCV sources.

See #17827 and opencv/opencv-python#356

Workaround: build from sources directly.

[Rylangrayston]

Thankyou alalek!