how to make Tb3 follower demo have obstacle avoidance

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I have to make the turtlebot3 to follow a vehicle and I have change the range of the angle so it will follow at the left back of the vehicle..Then , I am not sure what is the suitable coding for the obstacle avoidance and where to put it inside this code: Hope someone can help me as soon as possible cause it was my final year project

import rospy import os import pickle from sensor_msgs.msg import LaserScan from geometry_msgs.msg import Twist import numpy as np

class follower: def __init__(self): rospy.loginfo('Follower node initialized') self.config_dir = os.path.join(os.path.dirname(__file__)) self.config_dir = self.config_dir.replace('nodes', 'config') self.pub = rospy.Publisher('cmd_vel', Twist, queue_size = 1) self.clf = pickle.load(open(self.config_dir + '/clf', "rb")) self.clf2 = pickle.load(open(self.config_dir + '/clf2', "rb")) self.labels = {'30_0':0, '30_l':1, '30_r':2, '45_0':3, '45_l':4, '45_r':5,'15_0':6, 'empty':7} rospy.loginfo('Tree initialized') self.follow()

def check_people(self):
    laser_data=[]
    laser_data_set=[]
    result=[]
    ret = 0
    self.msg = rospy.wait_for_message("scan_filtered", LaserScan)

    for i in range(50,-2,-1) + range(359, 269,-1):

        if   np.nan_to_num( self.msg.intensities[i] ) != 0 :
             laser_data.append(np.nan_to_num(self.msg.intensities[i]))

        elif (i+1) in range(50,-2,-1) + range(359, 269,-1) and (i-1) in range(50,-2,-1) + range(359, 269,-1) and np.nan_to_num(self.msg.intensities[i]) == 0:
             laser_data.append((np.nan_to_num(self.msg.intensities[i+1])+np.nan_to_num(self.msg.intensities[i-1]))/2)

        else :
             laser_data.append(np.nan_to_num(self.msg.intensities[i]))

    laser_data_set.append(laser_data)

    [x for (x , y) in self.labels.iteritems() if y == self.clf2.predict(laser_data_set) ] ## Predict the position

    if result == ['empty']:
        ret = 0

    else:
        ret = 1

    return ret

def laser_scan(self):
    data_test=[]
    data_test_set=[]
    self.msg = rospy.wait_for_message("scan_filtered", LaserScan)

    for i in range(50,-2,-1) + range(359, 269,-1):

        if   np.nan_to_num( self.msg.ranges[i] ) != 0 :
             data_test.append(np.nan_to_num(self.msg.ranges[i]))

        elif (i+1) in range(50,-2,-1) + range(359, 269,-1) and (i-1) in range(50,-2,-1) + range(359, 269,-1) and np.nan_to_num(self.msg.ranges[i]) == 0:
             data_test.append((np.nan_to_num(self.msg.ranges[i+1])+np.nan_to_num(self.msg.ranges[i-1]))/2)

        else :
             data_test.append(np.nan_to_num(self.msg.ranges[i]))

    data_test_set.append(data_test)

    return [x for (x , y) in self.labels.iteritems() if y == self.clf.predict(data_test_set) ] 

def follow(self):
    while not rospy.is_shutdown():
        check = self.check_people()
        if  check == 1:
            x = self.laser_scan()
            twist = Twist()
            ## Do something according to each position##
            if  x == ['30_0']:
                twist.linear.x  = 0.18;         twist.angular.z = 0.0;
            elif x== ['30_l']:
                twist.linear.x  = 0.13;         twist.angular.z = 0.4;
            elif x== ['30_r']:
                twist.linear.x  = 0.13;         twist.angular.z = -0.4;
            elif x== ['45_0']:
                twist.linear.x  = 0.18;         twist.angular.z = 0.0;
            elif x== ['45_l']:
                twist.linear.x  = 0.13;         twist.angular.z = 0.3;
            elif x== ['45_r']:
                twist.linear.x  = 0.13 ...