publish 2d pose

#!/usr/bin/env python
import rospy
from turtlesim.msg import Pose
from nav_msgs.msg import Odometry
from tf.transformations import euler_from_quaternion
from math import degrees, pi


class TB3Pose2D:
    def __init__(self):
        rospy.init_node('pub_tb3_pose', anonymous = True)
        rospy.Subscriber('/odom', Odometry, self.get_odom)

        self.pub = rospy.Publisher('/tb3pose', Pose, queue_size = 10)        
        self.tb3pose2d = Pose()
        self.previous_angle = 0.0           # angular position range (0, 2pi) radinans 
        self.angular_displacement = 0.0     # angular displacement range (-inf, +inf) radians

    def get_odom(self, dat):          # when this function is being runned, theta is fixed
        pos_x, pos_y, current_angle = self.get_pose(dat)   # from function 'get_pose' gain euler theta and 2d coordinate info 
        
        pose2d       = Pose()   # make instance which has type of Pose  
        pose2d.x     = pos_x
        pose2d.y     = pos_y
        pose2d.linear_velocity  = dat.twist.twist.linear.x
        pose2d.angular_velocity = dat.twist.twist.angular.z
        
        delta_angle = current_angle - self.previous_angle
        if delta_angle >  5.0:          # this conditon is about situation of passing discontinuous point (0 or 2pi)
            delta_angle -= 2 * pi       # during subscribe to subscribe delta angle is less than (2pi-5) rad = 73 deg 
        elif delta_angle < -5.0:
            delta_angle += 2 * pi
        else:
            pass

        self.previous_angle = current_angle         # initialize previous angle as current angle
        self.angular_displacement += delta_angle

        pose2d.theta = self.angular_displacement
        self.tb3pose2d = pose2d;    self.pub.publish(self.tb3pose2d)

    def get_pose(self, msg):
        q = (msg.pose.pose.orientation.x, msg.pose.pose.orientation.y,
             msg.pose.pose.orientation.z, msg.pose.pose.orientation.w)

        quart = euler_from_quaternion(q)
        theta = quart[2]        # theta is range from -pi to pi

        if theta < 0:           # make theta (azimuth angle) range from [-pi, pi] to [0, 2pi]
            theta += 2 * pi

        pos_x = msg.pose.pose.position.x
        pos_y = msg.pose.pose.position.y
        
        return pos_x, pos_y, theta


if __name__ == '__main__':
    try:
        TB3Pose2D()
        rospy.spin()
        
    except rospy.ROSInterruptException:  pass