# Ttn - json -python (paho-mqtt)

**URL:** <https://www.thethingsnetwork.org/forum/t/ttn-json-python-paho-mqtt/16673>\
**Category:** Uncategorized\
**Created:** [August 8, 2018, 5:42pm UTC](https://www.thethingsnetwork.org/forum/t/ttn-json-python-paho-mqtt/16673 "2018-08-08T17:42:02Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![dynamitron](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/dynamitron/32/35697_2.png) [@dynamitron](https://www.thethingsnetwork.org/forum/u/dynamitron)\
**Post date:** [August 8, 2018, 5:42pm UTC](https://www.thethingsnetwork.org/forum/t/ttn-json-python-paho-mqtt/16673/1 "2018-08-08T17:42:02Z")

</div>

I an new from few day in ttn, so be patient with me.  
I have a device which send a 2 bytes counter value.  
I have the following payload decoder which work when I am testing it :

```auto
function Decoder(bytes, port) 
  {
    value = (bytes[0] << 8)|bytes[1];
    
    return {
      "value": String(value)
     }
  }
```

example :

payload = 64 64  
result :  
{  
“value”: “25700”  
}

After I use paho.mqtt in ptyhon scipt located on a remote raspberry.  
Each time the script receives a upling it crash and says “TypeError: the JSON object must be str, not 'bytes”

Could someone tell me what is happening ?  
The problem is on the ttn side or the python side.  
all suggestion are welcomed and many thank in advance !!!

```auto
#! /usr/bin/env Python3.4
# -*- coding: UTF-8 -*-

import paho.mqtt.client as mqtt
import json
import base64

APPEUI = "ABCDEFABCDEF0000"
APPID = "dynamitron_test"
PSW = 'ttn-account-v2.iNmvcWKseHAcqZ8z5BEBS8PpmZ86ePfBArQchAOppFc'

#Call back functions 

# gives connection message
def on_connect(mqttc, mosq, obj,rc):
    print("Connected with result code:"+str(rc))
    # subscribe for all devices of user
    mqttc.subscribe('+/devices/#')

# gives message from device
def on_message(mqttc,obj,msg):
    x = json.loads(msg.payload)
    device = x["dev_id"]
    payload_raw = x["payload_raw"]
    payload_plain = base64.b64decode(payload_raw)
    datetime = x["metadata"]["time"]
    #rssi = x["metadata"]["gateways"]["rssi"] # <== this raises an error (why?)
    rssi = -1
    print(device + ": " + payload_raw + " ==> " + payload_plain + ", RSSI ["+ str(rssi) + "] @" + datetime )

def on_publish(mosq, obj, mid):
    print("mid: " + str(mid))

def on_subscribe(mosq, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))

def on_log(mqttc,obj,level,buf):
    print("message:" + str(buf))
    print("userdata:" + str(obj))
    
mqttc= mqtt.Client()
# Assign event callbacks
mqttc.on_connect=on_connect
mqttc.on_message=on_message

mqttc.username_pw_set(APPID, PSW)
mqttc.connect("eu.thethings.network",1883,60)

# and listen to server
run = True
while run:
    mqttc.loop()
```

---

<div class="post-metadata">

**Author:** ![kersing](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/kersing/32/44777_2.png) [@kersing](https://www.thethingsnetwork.org/forum/u/kersing)\
**Post date:** [August 8, 2018, 8:40pm UTC](https://www.thethingsnetwork.org/forum/t/ttn-json-python-paho-mqtt/16673/2 "2018-08-08T20:40:19Z")

</div>

> [@dynamitron](#):
>
> I an new from few day in ttn, so be patient with me.

Being new does not mean you don’t have to format your messages. Next time use the hints [posted here](https://www.thethingsnetwork.org/forum/t/how-do-i-format-my-forum-post/8735) to improve readability.