Pi Zero MQTT Sensor Node with Mosquitto and paho-mqtt in Python

# gpiozero and lgpio come from Raspberry Pi OS itself; the venv can see them
# only if it was created with --system-site-packages (as in the BME280 tutorial):
#   python3 -m venv --system-site-packages ~/envs/sensors
source ~/envs/sensors/bin/activate
pip install 'paho-mqtt>=2.0' RPi.bme280 smbus2

#!/usr/bin/env python3
"""Raspberry Pi Zero MQTT sensor node (paho-mqtt 2.x)."""
import json
import time

import bme280
import smbus2
import paho.mqtt.client as mqtt
from gpiozero import LED

BROKER = '192.168.1.20'     # IP or hostname of the Mosquitto broker
PORT = 1883
USER, PASSWORD = 'sensor', 'your-password'
NODE = 'pizero1'
T_ENV = f'home/{NODE}/env'
T_STATUS = f'home/{NODE}/status'
T_LED = f'home/{NODE}/led/set'
INTERVAL_S = 30

led = LED(17)
bus = smbus2.SMBus(1)
cal = bme280.load_calibration_params(bus, 0x76)

def on_connect(client, userdata, flags, reason_code, properties):
    if reason_code.is_failure:
        print('Connect failed:', reason_code)
        return
    print('Connected to broker')
    # Announce we are online (retained, so new subscribers see it)
    client.publish(T_STATUS, 'online', qos=1, retain=True)
    # Subscribe here so the subscription is renewed after every reconnect
    client.subscribe(T_LED, qos=1)

def on_message(client, userdata, msg):
    command = msg.payload.decode().strip().upper()
    if command == 'ON':
        led.on()
    elif command == 'OFF':
        led.off()
    print('LED command:', command)

client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2, client_id=NODE)
client.username_pw_set(USER, PASSWORD)
# Last will: published by the broker if we vanish without disconnecting
client.will_set(T_STATUS, 'offline', qos=1, retain=True)
client.on_connect = on_connect
client.on_message = on_message
client.reconnect_delay_set(min_delay=1, max_delay=60)

client.connect(BROKER, PORT, keepalive=60)
client.loop_start()  # network handling runs in a background thread

try:
    while True:
        d = bme280.sample(bus, 0x76, cal)
        payload = json.dumps({
            'temperature_c': round(d.temperature, 2),
            'humidity_pct': round(d.humidity, 1),
            'pressure_hpa': round(d.pressure, 2),
            'ts': int(time.time()),
        })
        client.publish(T_ENV, payload, qos=1, retain=True)
        time.sleep(INTERVAL_S)
except KeyboardInterrupt:
    pass
finally:
    # A clean disconnect does NOT trigger the will, so publish offline ourselves
    client.publish(T_STATUS, 'offline', qos=1, retain=True).wait_for_publish()
    client.loop_stop()
    client.disconnect()