Simple implmentation of a ros node in python

ros_simple_sample.py

#!/usr/bin/python
import rospy
from std_msgs.msg import String
from sensor_msgs.msg import Image

import cv2
import numpy as np

class FaceFinder:
    def __init__(self):
        rospy.init_node("face_finder_node", anonymous=True)

        self.bridge = CvBridge()
        self.image_sub = rospy.Subscriber("IMAGE_TOPIC_HERE", Image, self.image_callback)
        self.frame = None   # Initialize image frame to None

    def image_callback(self, data):
        try:
            self.frame = self.bridge.imgmsg_to_cv2(data, "bgr8")
        except CvBridgeError as e:
            print(e)

    def find_smile(self):
        if self.frame == None:
            return

        #### Face/smile finding code here

    def run(self):
        # Set detector rate to 10hz
        r = rospy.Rate(10)
        while not rospy.is_shutdown():
            self.find_smile()   # Run smile detector code once
            r.sleep()           # Sleep until time is up for next cycle to hit 10hz

if __name__ == "__main__":
    face_finder = FaceFinder()
    face_finder.run()