[python] how the vehilce keep moving, while the if condition doesnot receive any value?! [closed]

edit

In the following code, i want the robot keep moving up to the time that the if condition gets True. Now the problem is that, when one of the conditions in if, receives no value (ValueError: min() arg is an empty sequence), the vehicle does not start moving.how can i define such a condition?

(Note: min() is generated by another python code and provides value for self.object_1. when i move the vehicle for far, it does not have value, up to the time that the vehicle gets close to the object.)

#!/usr/bin/env python
import rospy
from find_object_2d.msg import DetectionInfo
from sensor_msgs.msg import LaserScan
from std_msgs.msg import Int32, Float32, String, Time, Int8, Float64
from geometry_msgs.msg import Twist
import numpy as np
from geometry_msgs.msg import Pose


class object_detection_dist_to_goal():
    def __init__(self):
        self.velocity_publisher = rospy.Publisher('/cmd_vel', Twist, queue_size = 1)
        self.distance_to_object_publisher = rospy.Publisher('/distance_to_object', Float64, queue_size = 10)
        rospy.Subscriber('/info', DetectionInfo, self.infocallback)
        rospy.Subscriber('lidar_distance',Pose, self.tfcallback)

        self.move = Twist()
        self.object = Pose()
    def tfcallback(self, msg):
        self.object = msg
        #print(self.object)
        self.object_1 = self.object.position.x
        print("object_1", self.object_1)

    def infocallback(self, msg):
        inlier_id = msg.ids
        self.length = len(inlier_id)

        self.move.linear.x = 0.25 
        if (self.length == 2) and (self.object_1 < 5.4):
            self.move.linear.x = 0.0
            print("vehicle stopped: ", self.move.linear.x)
        self.velocity_publisher.publish(self.move)

    def loop(self):
        rospy.spin()

if __name__ == '__main__':
    rospy.init_node('ontrack_cameralidar', anonymous=False)  #anony=False
    on_track_camer_lidar = object_detection_dist_to_goal()
    on_track_camer_lidar.loop()

Sorry, i have provided the other python code that generates the min value. I think i should solve the error here first:

#!/usr/bin/env python
from roslib import message
import rospy
import sensor_msgs.point_cloud2 as pc2
from sensor_msgs.msg import PointCloud2, PointField
import numpy as np
import ros_numpy
from geometry_msgs.msg import Pose

#listener
def listen():
    rospy.init_node('listen', anonymous=True)
    rospy.Subscriber("/Filtered_points_x", PointCloud2, callback_kinect)


def callback_kinect(data):
    pub = rospy.Publisher('lidar_distance',Pose, queue_size=10)
    data_lidar = Pose()
    xyz_array = ros_numpy.point_cloud2.pointcloud2_to_xyz_array(data)
    print(xyz_array)
    mini_data = min(xyz_array[:,0])
    print("mini_data", mini_data)
    data_lidar.position.x = mini_data  
    pub.publish(data_lidar) 
    print("data_points", data_lidar.position.x)
    height =  int (data.height / 2)
    middle_x = int (data.width / 2)
    middle = read_depth (middle_x, height, data)  # do stuff with middle


def read_depth(width, height, data) :
    if (height >= data.height) or (width >= data.width) :
        return -1
    data_out = pc2.read_points(data, field_names= ('x','y','z'), skip_nans=True, uvs=[[width, height]])
    int_data = next(data_out)
    rospy.loginfo("int_data " + str(int_data))
    return int_data

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

Here, i have limited the input of the subscriber. i mean when the vehicle is near to the objects, it receives a limited data points, and when i start moving the vehicle far from the objects it does not receive any value and shows the following error:

[[ 7.99410915  1.36072445 -0.99567264]]
('mini_data', 7.994109153747559)
('data_points', 7.994109153747559)
[INFO] [1662109961.035894]: int_data (7.994109153747559, 1.3607244491577148, -0.9956726431846619 ...