Connecting M2MQTT Paho Python Client to AWS IoT

I am having difficulty connecting to AWS IoT with the following Python script. I followed AWS IoT Core console and created a Thing and Security Certificate, then created policy and attached it certificate, then attached certificate to a Thing. Eventually I downloaded private key PEM, security certificate PEM and CA certificates (AmazonRootCA1.crt and AmazonCARoot3.crt).

So here is the script - there is no errors generated when I run it - it simply keeps waiting for server response...

Any help or clue would be greatly appreciated. I had no problem connecting to AWS IoT with C# client that I wrote which in addition to CA certificate required private key in .PFX format which I created...

#! /usr/bin/python3.5
import serial
import time
import datetime
import os
import socket
import ssl
import logging
import paho.mqtt.client as mqtt
import sys
print(sys.executable)

def on_disconnect(client, userdata, rc):
if rc==0:
print("client disconnected OK")
client.connected_flag=False
#client.disconnect_flag=True

def on_connect(client, userdata, flags, rc):
if rc==0:
print("Connected OK")
mqtt.Client.connected_flag=True
mqtt.Client.bad_connection_params=False
else:
mqtt.Client.bad_connection_params=True

    if rc==1:  
        print("Failed to connect. Connection refused, unacceptable protocol version. Error Code=", rc)  
    elif rc==2:  
        print("Failed to connect.Connection refused, identifier rejected. Error Code=", rc)  
    elif rc==3:  
        print("Failed to connect.Connection refused, server unavailable. Error Code=", rc)  
    elif rc==4:  
        print("Failed to connect.Connection refused, bad user name or password. Error Code=", rc)  
    elif rc==5:  
        print("Failed to connect.Connection refused, not authorized. Error Code=", rc)  

    rpiclient.loop_stop()  
    sys.exit()  

def on_publish(client, userdata, mid):
if rc==0:
print("Data published OK: ", userdata)
else:
print("Failed to publish data. MessageID=", mid)
pass

broker="xxxxxxxxxxxxxxxx-ats.iot.us-west-2.amazonaws.com"
port=8883

rpiclient = mqtt.Client("GravityStorms", clean_session=True, userdata=None, protocol=MQTTv311, transport="tcp")

caCertPath = "./AmazonRootCA1.crt"
clientCertFilePath = "./xxxxxxxxxx-certificate.pem.crt"
keyFilePath = "./xxxxxxxxxx-private.pem.key"
rpiclient.tls_set(caCertPath,
certfile=clientCertFilePath,
keyfile=keyFilePath,
cert_reqs=ssl.CERT_REQUIRED,
tls_version=ssl.PROTOCOL_TLSv1_2,
ciphers=None)

rpiclient.tls_insecure_set(False)

mqtt.Client.connected_flag = False

mqtt.Client.bad_connection_params=False

rpiclient.on_connect = on_connect

rpiclient.on_publish = on_publish

rpiclient.on_disconnect = on_disconnect

rpiclient.loop_start()

rpiclient.will_set("dwm/position", "Client PahoClient-on-RPi2 had unexpectedly disconnected", 1, True)

try:
print("Connecting to MQTT broker ",broker)
rpiclient.connect(broker, port, keepalive=60)
time.sleep(1)

print("mqtt.Client.connected_flag={}, mqtt.Client.bad_connection_params={}".format(mqtt.Client.connected_flag, mqtt.Client.bad_connection_params))  
while mqtt.Client.connected_flag == False and mqtt.Client.bad_connection_params == False:  
    print("Waiting for connection...");  
    time.sleep(1)  
if mqtt.Client.bad_connection_params == True:  
    rpiclient.loop_stop()  
    sys.exit()  
      

except Exception as ex:
print("Connection to MQTT Broker failed: ", ex)
rpiclient.loop_stop()
sys.exit()

rpiclient.loop_stop()

rpiclient.disconnect()