mqttwrapper

A little glue package to make it simple to quickly put together scripts that bridge MQTT and other libraries. See examples below.

Installation

Install from PyPI:

$ pip install mqttwrapper

paho-mqtt is used as the underlying MQTT library.

Usage

mqttwrapper.run_script handles the setup/maintenance of the MQTT connection and subscriptions to topics, and calls a callback function when messages are received. It can run in blocking mode where it will take care of the MQTT client handling or in non blocking mode where a new thread takes care this leaving your main thread free for other things.

The simplest script looks something like this:

from mqttwrapper import run_script

def callback(topic, payload):
    print("Received payload {} on topic {}".format(payload, topic))

def main():
    run_script(callback, broker="mqtt://127.0.0.1", topics=["my/awesome/topic1", "another/awesome/topic2"])

or in non blocking mode:

def main():
    run_script(callback, broker="mqtt://127.0.0.1", topics=["my/awesome/topic1", "another/awesome/topic2"], blocking=False)
    while True:
        echo "Alive and kicking"
        time.sleep(1)

Most extra keyword arguments passed to run_script are passed back to the callback function when it's called:

from mqttwrapper import run_script

def callback(topic, payload, context, foo):
    assert context == "hello"
    assert foo == "bar"
    print("Received payload {} on topic {}".format(payload, topic))

def main():
    run_script(callback, broker="mqtt://127.0.0.1", topics=["my/awesome/topic1", "another/awesome/topic2"], context="hello", foo="bar")

However some are reserved and will be consumed by `run_script` to configure how the MQTT connection behaves:

• broker (default MQTT_BROKER from environment, otherwise None): broker URL, e.g mybroker, mqtts://securebroker:8884, mqtt://username:password@coolbroker.example.org
• topics (default MQTT_TOPICS from environment, otherwise None): list of topics to subscribe to
• ignore_retained (default False): whether to ignore a received message if it was marked as retained
• blocking (default True): run in blocking or threaded mode
• client_id (default "",): client ID to use when connecting to broker
• clean_session (default True): whether to use a clean session upon (re)connect, or resume previous session. client_id must be provided if True
• qos (default 0): QoS to use for connection
• raise_exceptions (default False): whether to raise exceptions that occur during callback execution

If you don't need any context passed to your callback, just the topic and payload of messages, you can run in 'importless' mode by creating a callback module which has a callback function defined, then execute the mqttwrapper.run module:

$ cat callback.py
def callback(topic, payload):
    print(topic, payload)

$ python -m mqttwrapper.run

Retained messages

You can ignore MQTT retained messages by passing ignore_retained=True when calling run_script.

Publishing messages from the callback

Sometimes your callback function might want to publish its own MQTT messages, perhaps in reply to or an acknowledgement of a received message. This is possible by returning an iterable of (topic, payload) tuples from the callback, e.g.:

def callback(topic, payload):
  print("Received payload {} on topic {}".format(payload, topic))
  return [
    ("{}/ack".format(topic), payload)
  ]

mqttwrapper will take care of publishing these messages to the broker.

These tuples can optionally take the form (topic, payload, True) if you want the published message to be marked as retained.

NB any exceptions raised during execution of the callback will be logged and ignored, unless raise_exceptions=True is passed to run_script.

Configuration

broker and topics can be omitted from the run_script call and environment variables used instead:

• MQTT_BROKER: MQTT broker to connect to, e.g. mqtt://127.0.0.1/
• MQTT_TOPICS: Comma-separated list of topics to subscribe to, e.g. my/topic1,my/topic2

Examples

• rxv2mqtt