---
layout: page
title: "Basic MQTT Example"
description: ""
date: 2016-02-07 12:13
sidebar: true
comments: false
sharing: true
footer: true
ha_category: Custom Python Component Examples
---

<p class='note'>
This example requires you to have the [MQTT component](/components/mqtt/) up and running.
</p>

This is a simple hello world example to show the basics of using MQTT in a custom component. To use this example, create the file `<config dir>/custom_components/hello_mqtt.py` and copy the below example code.

This example follows a topic on MQTT and updates the state of an entity to the last message received on that topic. It will also register a service 'set_state' that will publish a message to the MQTT topic that we're listening to.

```python
import homeassistant.loader as loader

# The domain of your component. Should be equal to the name of your component.
DOMAIN = "hello_mqtt"

# List of component names (string) your component depends upon.
DEPENDENCIES = ['mqtt']


CONF_TOPIC = 'topic'
DEFAULT_TOPIC = 'home-assistant/hello_mqtt'


def setup(hass, config):
    """Setup the Hello MQTT component."""
    mqtt = loader.get_component('mqtt')
    topic = config[DOMAIN].get('topic', DEFAULT_TOPIC)
    entity_id = 'hello_mqtt.last_message'

    # Listener to be called when we receive a message.
    def message_received(topic, payload, qos):
        """A new MQTT message has been received."""
        hass.states.set(entity_id, payload)

    # Subscribe our listener to a topic.
    mqtt.subscribe(hass, topic, message_received)

    # Set the intial state
    hass.states.set(entity_id, 'No messages')

    # Service to publish a message on MQTT.
    def set_state_service(call):
        """Service to send a message."""
        mqtt.publish(hass, topic, call.data.get('new_state'))

    # Register our service with Home Assistant.
    hass.services.register(DOMAIN, 'set_state', set_state_service)

    # Return boolean to indicate that initialization was successfully.
    return True
```

Load the component by adding the following to your `configuration.yaml`. When your component is loaded, a new entity should popup and there should be a new service available to call.

```yaml
# configuration.yaml entry
hello_mqtt:
  topic: some_mqtt/topic/here
```

You can call the service with example payload:

```json
{
  "new_state": "some new state"
}
```