import cv2
#events = [i for i in dir(cv2) if 'EVENT' in i]
import numpy as np

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


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()