使用 mqtt 将两个值与 python 进行比较

Question

I'm trying to compare two values received from mqtt and send a publish message depending of the comparation. After searching a lot I get it working when I only compar if the two values are equal o diferent. But, what I really want to do is that when I receive a message, the program keep it (value of 230 for example), then if the new one is of the same condition( value of 250, still less than 300), so no action is required, till the value received is bigger than 300.

any suggestion of how to do it? I don't need a direct answer but if you know where I can look to more information or examples like what I'm trying to do it will be helpfull.

import paho.mqtt.client as mqtt
import time

client = mqtt.Client()
client.connect("test.mosquitto.org", 1883)

def on_connect(client, userdata, flags, rc):
    client.subscribe("Medir")

client.publish("Valve_OC", "Cerrar")
print("cierre de la valvula")
#initialize the new and last value
new_value=0
last_value = 0 
print("initial values: ", new_value, last_value)

def on_message_medir(client, userdata, message):  # The callback for when a PUBLISH message is received from topic MEDIR.
    global new_value
    global last_value
    new_value=int(float(str(message.payload.decode("utf-8"))))
    print("new_value:", new_value)
    compar_value(new_value, last_value) #function to compare the values

def compar_value(new_value, last_value): 
    if new_value != last_value:
        if new_value<300:
            client.publish("Valve_OC", "Abrir,100")
            last_value = new_value
            time.sleep(3)
        
        elif (new_value>300): 
            client.publish("Valve_OC", "Abrir,60")
            last_value=new_value       
            time.sleep(3)
       
def on_publish(client, obj, mid):
    print("Mensaje: " + str(mid))
def on_subscribe(client, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))
def on_log(client, obj, level, string):
    print(f"Log: {string}")
client = mqtt.Client()
client.on_connect = on_connect
client.on_publish = on_publish
client.message_callback_add("Medir", on_message_medir)
client.on_subscribe = on_subscribe
client.on_log = on_log
client.connect("test.mosquitto.org", 1883)

client.loop_forever()

Answer 1

You should just keep comparing the value, probably converting it to an int before comparing. Like this:

def compar_value(new_value): 
    if int(new_value) < 300:
        client.publish("Valve_OC", "Abrir,100")
        last_value = new_value
    else
        last_value = new_value

and when the message comes, you compare the value. And if you want to keep the last value, just keep updating the last_value variable, that sould be global.

I think you don't need the global redeclaration part when inside the function, since your variables are already globally delcared. Besides the sleep part also doesn't does any help, since the MQTT messages are all asynchronous.