cv2 and pyqt4 can't work together

Question

I try to use cv2 with PyQt4 widget but I keep getting this error:

(python3:3974): GLib-GObject-WARNING **: 12:41:27.117: cannot register existing type 'GdkDisplayManager'

(python3:3974): GLib-CRITICAL **: 12:41:27.118: g_once_init_leave: assertion 'result != 0' failed

(python3:3974): GLib-GObject-CRITICAL **: 12:41:27.118: g_object_new_with_properties: assertion 'G_TYPE_IS_OBJECT (object_type)' failed

I am sure my cv2 code works fine

import cv2
def takePicture():
    cap = cv2.VideoCapture(1)
    while(True):
        ret, frame= cap.read()
        cv2.imshow('frame', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    cap.release()
    cv2.destroyAllWindows()

but when I connect a button to it I get the previous error:

from PyQt4 import QtGui
 app = QtGui.QApplication(sys.argv)
 take_picture_button = QtGui.QPushButton('Take picture')
 from takePicture import takePicture
 take_picture_button.clicked.connect(takePicture)
 take_picture_button.show()

• Ubuntu 18.04
• python3.6.7
• PyQt4 ?
• cv2 ?