How to use MQTT in Python (Paho)
Tags: python, tutorial, mqtt, paho
Published: 2022-06-13 07:14:59

[Python](https://www.python.org/) is an interpreted, high-level, general-purpose programming language. Created by Guido van Rossum and first released in 1991, Python's design philosophy emphasizes code readability with its notable use of significant whitespace. Its language constructs and object-oriented approach aim to help programmers write clear, logical code for small and large-scale projects.[^1]

[MQTT](https://www.emqx.com/en/mqtt) is a kind of **lightweight IoT messaging protocol** based on the publish/subscribe model, which can provide real-time and reliable messaging service for IoT devices, only using very little code and bandwidth. It is suitable for devices with limited hardware resources and the network environment with limited bandwidth. Therefore, [MQTT protocol](https://www.emqx.com/en/mqtt) is widely used in IoT, mobile internet, IoV, electricity power, and other industries.

This article mainly introduces how to use the **paho-mqtt** client and implement connection, subscribe, messaging, and other functions between the [MQTT client](https://www.emqx.com/en/mqtt-client-sdk) and [MQTT broker](https://www.emqx.io), in the Python project.



## Project Initialization

This project uses Python 3.6 to develop and test. Readers can use the following command to confirm the Python version.

```
➜  ~ python3 --version             
Python 3.6.7
```

### Choose the MQTT Client

The [Paho Python Client](https://www.eclipse.org/paho/clients/python/) provides a client class with support for both MQTT v3.1 and v3.1.1 on Python 2.7 or 3.x. It also provides some helper functions to make publishing one off messages to an MQTT server very straightforward.

### Using Pip to Install the Paho MQTT Client

Pip is a management tool for the Python package. This tool provides find, download, install and uninstall functions for Python package.

```bash
pip3 install paho-mqtt
```



## The Use of Python MQTT

### Connect to the MQTT Broker

This article will use [the free public MQTT broker](https://www.emqx.com/en/mqtt/public-mqtt5-broker) provided by EMQX. This service is based on [MQTT IoT cloud platform](https://www.emqx.com/en/cloud) to create. The accessing information of the broker is as follows:

- Broker: **broker.emqx.io**
- TCP Port: **1883**
- Websocket Port: **8083**

#### Import the Paho MQTT Client

```python
from paho.mqtt import client as mqtt_client
```

#### Set the Parameter of MQTT Broker Connection

Set the address, port and topic of MQTT Broker connection. At the same time, we call the Python function `random.randint` to randomly generate the MQTT client id.

```python
broker = 'broker.emqx.io'
port = 1883
topic = "/python/mqtt"
client_id = f'python-mqtt-{random.randint(0, 1000)}'
# username = 'emqx'
# password = 'public'
```

#### Write the MQTT Connect Function

Write the connect callback function `on_connect`. This function will be called after connecting the client, and we can determine whether the client is connected successfully according to `rc` in this function. Usually, we will create an MQTT client at the same time and this client will connect to `broker.emqx.io`.

```python
def connect_mqtt():
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)
    # Set Connecting Client ID
    client = mqtt_client.Client(client_id)
    client.username_pw_set(username, password)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client
```

### Publish Messages

First, we define a while loop. In this loop, and we will set the MQTT client `publish` function to send messages to the topic `/python/mqtt` every second.

```python
 def publish(client):
     msg_count = 0
     while True:
         time.sleep(1)
         msg = f"messages: {msg_count}"
         result = client.publish(topic, msg)
         # result: [0, 1]
         status = result[0]
         if status == 0:
             print(f"Send `{msg}` to topic `{topic}`")
         else:
             print(f"Failed to send message to topic {topic}")
         msg_count += 1
```

### Subscribe

Write the message callback function `on_message`. This function will be called after the client received messages from the MQTT Broker. In this function, we will print out the name of subscribed topics and the received messages. 

```python
def subscribe(client: mqtt_client):
    def on_message(client, userdata, msg):
        print(f"Received `{msg.payload.decode()}` from `{msg.topic}` topic")

    client.subscribe(topic)
    client.on_message = on_message
```

### The Full Code

 **The Code of Publishing Messages** 

```python
# python 3.6

import random
import time

from paho.mqtt import client as mqtt_client


broker = 'broker.emqx.io'
port = 1883
topic = "python/mqtt"
# generate client ID with pub prefix randomly
client_id = f'python-mqtt-{random.randint(0, 1000)}'
# username = 'emqx'
# password = 'public'

def connect_mqtt():
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)

    client = mqtt_client.Client(client_id)
    client.username_pw_set(username, password)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client


def publish(client):
    msg_count = 0
    while True:
        time.sleep(1)
        msg = f"messages: {msg_count}"
        result = client.publish(topic, msg)
        # result: [0, 1]
        status = result[0]
        if status == 0:
            print(f"Send `{msg}` to topic `{topic}`")
        else:
            print(f"Failed to send message to topic {topic}")
        msg_count += 1


def run():
    client = connect_mqtt()
    client.loop_start()
    publish(client)


if __name__ == '__main__':
    run()

```

**The Code of Subscribing**

```python
# python3.6

import random

from paho.mqtt import client as mqtt_client


broker = 'broker.emqx.io'
port = 1883
topic = "python/mqtt"
# generate client ID with pub prefix randomly
client_id = f'python-mqtt-{random.randint(0, 100)}'
# username = 'emqx'
# password = 'public'


def connect_mqtt() -> mqtt_client:
    def on_connect(client, userdata, flags, rc):
        if rc == 0:
            print("Connected to MQTT Broker!")
        else:
            print("Failed to connect, return code %d\n", rc)

    client = mqtt_client.Client(client_id)
    client.username_pw_set(username, password)
    client.on_connect = on_connect
    client.connect(broker, port)
    return client


def subscribe(client: mqtt_client):
    def on_message(client, userdata, msg):
        print(f"Received `{msg.payload.decode()}` from `{msg.topic}` topic")

    client.subscribe(topic)
    client.on_message = on_message


def run():
    client = connect_mqtt()
    subscribe(client)
    client.loop_forever()


if __name__ == '__main__':
    run()
```




## Test

### Publish Messages

Run the code of publishing messages, we will see  that the client connects successfully and publishes messages successfully

```bash
python3 pub.py
```

![python publish mqtt messages](https://assets.emqx.com/images/8087a35e3b4c6e11e3b432dac024c420.png)

#### Subscribe

Run the code of subscribing to messages, we will see  that the client connects successfully and receives the published messages successfully

```bash
python3 sub.py
```

![python mqtt subscribe](https://assets.emqx.com/images/24fa48443372da483f06f9cce06b32bc.png)


## Summary

So far, we have finished that use the **paho-mqtt** client to connect to [the free public MQTT broker](https://www.emqx.com/en/mqtt/public-mqtt5-broker), and implemented the connect, publish messages and subscribe to messages between the test client and MQTT broker.

Python is different from the high-level languages like C++ or Java, it is more suitable for implementing the business logic on the device side. Using Python can reduce the logic complexity of code and reducing the cost of interaction with the device. We believe that Python will have wider applications in the field of IoT.

Next, we will publish more articles about IoT development and Python. Stay tuned.



[^1]: https://en.wikipedia.org/wiki/Python_(programming_language)