extract the time from /tf topic, between two specific frames

edit

@hank880907

#!/usr/bin/env python
from sqlite3 import Row
import rospy
import tf
from tf2_msgs.msg import TFMessage
from std_msgs.msg import Int32, Float32, String, Time
import csv


class tf_frames:
    def __init__(self, frame_id, child_frame_id):
        self.frame_id = frame_id
        self.child_frame_id = child_frame_id
        #listener = tf.TransformListener()
        TEXTFILE = open("data_publisher_47.csv", "w")
        TEXTFILE.truncate()
        def callback(msg):
            rospy.Subscriber('/tf', TFMessage, callback)
            if frame_id == "camera_color_optical_frame" and child_frame_id=="object_47":    
                time_stamp = msg.header.stamp
                row = [time_stamp]
                print (time_stamp)
                with open('data_publisher_47.csv', 'a') as csvfile:
                    writer = csv.writer(csvfile)
                    writer.writerow(row)
                    csvfile.close

        if __name__ == '__main__':
            tf_frames()

I have wriiten the upper code. but it is not working!!!

of course it won't work. You are not even initializing the ros node correctly... have you take a look at how to write a node in ros? https://wiki.ros.org/ROS/Tutorials/Wr...