使用python在open cv中使用鼠标事件绘制矩形或直线

I am trying to draw a straight line between two coordinates which would be obtained by clicking on the image or by mouse events. I am able to draw individual circles on clicking the mouse, but cannot figure out how to draw line between those points. When I am using this code, I can only print the start and end coordinates, not draw a line between them.I am trying to draw a straight line between two