How can i bridge and display images from realsense d435 camera?

edit

I am a beginner in ros. I am looking to get image frames from an Intel Realsense D435 camera, bridge and show the image (with opencv) . At the same time, I look to print/ log out the information from the camera. After running code, the program continuously runs (due to rospy.spin() function) but does not print out anything.

Where could I be going wrong with the code? Could someone please explain a bit on how to use the ros messages in a python code. I am writing a subscriber node.'

class Depth_Retriever():
    def __init__(self):

        self.bridge = CvBridge()

        self.sub = rospy.Subscriber('/camera/depth/image_rect_raw',Image,callback)

    def callback(self,ros_pics):
        try: 
            my_image = self.bridge.imgmsg_to_cv2(ros_pics, encoding = "passthrough")

        except CvBridgeError as e:
            print("CvBridge could not convert images from realsense to opencv")
        height,width, channels = my_image.shape
        my_height = my_image.shape[0]
        print(my_height)

        self.vert_len = ros_pics.height # retrieve height information from Image msg
        print(self.vert_len)


def main():
    rospy.init_node("Depth",anonymous = True)

    rospy.spin()


if __name__ == '__main__':

    main()

Thank you for help in advance.