MQTT and Python For Beginners -Publishing Messages

MQTT and Python For Beginners -Tutorials

 源自於 http://www.steves-internet-guide.com/mqtt-python-beginners-course/

發行訊息至broker

Main Client Methods

The paho mqtt client class has several methods.The main ones are:

• connect() and disconnect()
• subscribe() and unsubscribe()
• publish()

Each of these methods is associated with a callback. See Later.

Importing The Client Class

To use the client class you need to import it. Use the following:

Import paho.mqtt.client as mqtt

Creating a Client Instance

The client constructor takes 4 optional parameters, as shown below .but only the client_id is necessary, and should be unique.

Client(client_id=””, clean_session=True, userdata=None, protocol=MQTTv311, transport=”tcp”)

To create a instance use:

client =mqtt.Client(client_name)

Connecting To a Broker or Server

Before you can publish messages or subscribe to topics you need to establish a connection to a broker.

To do this use the connect method of the Python mqtt client.

The method can be called with 4 parameters. The connect method declaration is shown below with the default parameters.

connect(host, port=1883, keepalive=60, bind_address="")

Note: You only need to supply the broker name/IP address.

The general syntax is

client.connect(host_name)

公開 MQTT Borker

• ESP8266 连接到免费的公共 MQTT 服务器 - broker.emqx.io:1883
• test.mosquitto.org - test.mosquitto.org:1883
• Sandboxes | IoT development made simple - mqtt.eclipse.org:1883
• The Public MQTT Broker by HiveMQ - Check out our MQTT Demo - broker.hivemq.com:1883

Publishing Messages

Once you have a connection you can start to publish messages.

To do this we use the publish method.

The publish method accepts 4 parameters. The parameters are shown below with their default values.

publish(topic, payload=None, qos=0, retain=False)

The only parameters you must supply are the topic, and the payload.

The payload is the message you want to publish.

The general syntax is:

client.publish("house/light","ON")

Example Python Script:

We are now in a position to create our first Python Script to Publish a message.

The script below publishes the message OFF to topic house/main-light

import paho.mqtt.client as mqtt #import the client1
broker_address="192.168.1.184" 
#broker_address="iot.eclipse.org" #use external broker
client = mqtt.Client("P1") #create new instance
client.connect(broker_address) #connect to broker
client.publish("house/main-light","OFF")#publish

import time
import paho.mqtt.client as mqtt #import the client1
broker_address="broker.hivemq.com" 
#broker_address="iot.eclipse.org" #use external broker
client = mqtt.Client("P1") #create new instance
client.connect(broker_address) #connect to broker
client.publish("alex9ufo/house/main-light","OFF")#publish
print ("publish (alex9ufo/house/main-light,OFF")

time.sleep(10)

client.publish("alex9ufo/house/main-light","ON")#publish
print ("publish (alex9ufo/house/main-light, ON")