ServerSocket on Android Devices is rejecting incoming connection

Question

    public class MainActivity extends AppCompatActivity
{
    //https://stackoverflow.com/questions/11107258/serversocket-android
    private static String TAG = "ServerSocketTest";
    private ServerSocket server;
    Runnable conn = new Runnable()
    {
        public void run()
        {
            try
            {
                System.out.println("binding server to port");
                server = new ServerSocket(53000);

                while (true)
                {
                    Socket socket = server.accept();
                    System.out.println("Connection from : " + socket.getInetAddress());
                    BufferedReader in = new BufferedReader(
                            new InputStreamReader
                                    (socket.getInputStream()));
                    System.out.println("got input stream: " + in);
                    String str = in.readLine();
                    System.out.println("received response from server: " + str);
                    in.close();
                    socket.close();
                }
            } catch (IOException e) {
                System.out.println("error1: " + e.getMessage());
            } catch (Exception e) {
                System.out.println("error2: " + e.getMessage());
            }
        }
    };

}

Android Application that acts as a server is working however it is not accepting connection upon trying to establish a connection from python script. (The host refuse to establish a connection)

The same code was tested on a normal Java application and it works.