The Losant MQTT client provides a simple way for custom things to communicate with the Losant platform over MQTT. You can authenticate as a device, publish device state, and listen for device commands.
This client works with both Python 2.7 and 3. It uses the Paho MQTT Client under the covers for the actual MQTT communication.
The latest stable version is available in the Python Package Index (PyPi) and can be installed using
pip install losant-mqtt
Below is a high-level example of using the Losant Python MQTT client to send the value of a temperature sensor to the Losant platform.
import time
from losantmqtt import Device
# Construct device
device = Device("my-device-id", "my-app-access-key", "my-app-access-secret")
def on_command(device, command):
print("Command received.")
print(command["name"])
print(command["payload"])
# Listen for commands.
device.add_event_observer("command", on_command)
# Connect to Losant.
device.connect(blocking=False)
# Send temperature once every second.
while True:
device.loop()
if device.is_connected():
temp = call_out_to_your_sensor_here()
device.send_state({"temperature": temp})
time.sleep(1)
A device represents a single thing or widget that you'd like to connect to the Losant platform. A single device can contain many different sensors or other attached peripherals. Devices can either report state or respond to commands.
A device's state represents a snapshot of the device at some point in time. If the device has a temperature sensor, it might report state every few seconds with the temperature. If a device has a button, it might only report state when the button is pressed. Devices can report state as often as needed by your specific application.
Commands instruct a device to take a specific action. Commands are defined as a name and an optional payload. For example, if the device is a scrolling marquee, the command might be "update text" and the payload would include the text to update.
Device(device_id, key, secret, secure=True, transport="tcp")
The Device() constructor takes the following arguments:
- device_id
- The device's ID. Obtained by first registering a device using the Losant platform.
- key
- The Losant access key.
- secret
- The Losant access secret.
- secure
- If the client should connect to Losant over SSL - default is true.
- transport
- Allowed values are "tcp" and "websockets". Defaults to "tcp", which is a raw TCP connection over ports 1883 (insecure) or 8883 (secure). When "websockets" is passed in, connects using MQTT over WebSockets, which uses either port 80 (insecure) or port 443 (secure).
from losantmqtt import Device
device = Device("my-device-id", "my-app-access-key", "my-app-access-secret")
connect(blocking=True)
Connects the device to the Losant platform. Hook the connect event to know when a connection has been successfully established. Connect takes the following arguments:
- blocking
- If the connect method should block or not. True is the default, which means that the connect call will be a blocking call that will not return until the connection is closed or an error occurs - all interaction has to be done through the various event callbacks. If blocking is set to False, the function will only block until the connection is kicked off - after that point you must run the network loop yourself, by calling the loop method periodically.
is_connected()
Returns a boolean indicating whether or not the device is currently connected to the Losant platform.
close()
Closes the device's connection to the Losant platform.
send_state(state, time_like=None)
Sends a device state to the Losant platform. In many scenarios, device states will change rapidly. For example a GPS device will report GPS coordinates once a second or more. Because of this, sendState is typically the most invoked function. Any state data sent to Losant is stored and made available in data visualization tools and workflow triggers.
- state
- The state to send as a Dict.
- time_like
- When the state occurred - if None or not set, will default to now.
device.send_state({ "voltage": read_analog_in() })
loop(timeout=1)
Loops the network stack for the connection. Only valid to call when connected in non-blocking mode. Be sure to call this reasonably frequently when in that model to make sure the underlying MQTT connection does not get timed out.
- timeout
- Max time to block on the socket before continuing - defaults to 1 second.
add_event_observer(event_name, observer)
Adds an observer to listen for an event on this device.
- event_name
- The event to listen for. Possible events are: "connect" (the device has connected), "reconnect" (the device lost its connection and reconnected), "close" (the device's connection was closed), and "command" (the device has received a command from Losant).
- observer
- Callback method to call when the given event fires. The first argument for all callbacks will be the device instance. Command callbacks have a second argument - the command received.
def on_command(device, cmd):
print(cmd["time"]) # time of the command
print(cmd["name"]) # name of the command
print(cmd["payload"]) # payload of the command
device.add_event_observer("command", on_command)
remove_event_observer(event_name, observer)
Removes an observer from listening for an event on this device.
- event_name
- The event to stop listening for. Same events as add_event_observer.
- observer
- Callback method to remove.
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