How to Send and Receive JSON Data Over MQTT with Python

send-json-data-mqtt Encoding data in JSON is popular for sending data over the Internet, and also for storing data.

You can encode a Python List or dictionary in JSON format and then decode it back into a list or dictionary as illustrated in the diagram below:

send-json-data-diagram

Note: if you prefer video then I’ve create a YouTube video that covers this- How to Encode, Send and Receive JSON Data Using the Pythom MQTT Client

You will first need to import the json module

import json

To encode a python dictionary or list use json.dumps(data) as show below:

data_out=json.dumps(brokers_out) # encode object to JSON

To convert from a JSON string to a Python object use json.loads(json_string) as show below:

m_in=json.loads(m_decode) #decode json data

I’ve created a simple Python script that demonstrates the process.

The first part of the script encodes and decodes a Python Dictionary.

The second part of the script encodes a Python Dictionary Publishes the Data to the MQTT broker, then receives the data and decodes it back into a dictionary.

You can download the demo script using the link below

Python Send-Receive JSON Data Over MQTT 0.85 KB

Download

Here is a screen shot of what it looks like when run.

Notice the Python objects is converted to a string by the json.dumps() function.

Json-encode-decode-pytho

Now we run the second part of the script which publishes the JSON data and then receives the Data and decodes it back into a dictionary.

send-data-json-mqtt-example

Here is the on_message Callback which receives the messages and converts it to a dictionary.

def on_message(client, userdata, msg):
    topic=msg.topic
    m_decode=str(msg.payload.decode("utf-8","ignore"))
    print("data Received type",type(m_decode))
    print("data Received",m_decode)
    print("Converting from Json to Object")
    m_in=json.loads(m_decode) #decode json data
    print(type(m_in))
    print("broker 2 address = ",m_in["broker2"])