NameError：未定义名称“msg”

Question

def on_message(client, userdata, message):
    global msg
    #print("message received " ,str(message.payload.decode("utf-8")))
    #print("message topic=",message.topic)
    #print("message qos=",message.qos)
    #print("message retain flag=",message.retain)
    msg = str(message.payload)

broker_address="10.87.7.27"
print("creating new instance")
client = mqtt.Client("P1") #create new instance
client.on_message= on_message #attach function to callback
print("connecting to broker")
client.connect(broker_address,1883) #connect to broker
client.loop_start() #start the loop
print("Subscribing to topic","home/kitchen/output/lights/set")
client.subscribe("Sekurit_KTBlower_Optimizer_write")
time.sleep(10) 

print(msg)
dict_str = msg.decode("UTF-8")
#jsonload = json.loads(dict_str)
mydata = ast.literal_eval(dict_str)
Lowerpredict = mydata["Lowerpredict"]
Upperpredict = mydata["Upperpredict"]

print(Lowerpredict,UpperPredict)
client.loop_stop() #stop the loop

我收到一个错误，因为“NameError: name 'msg' is not defined” 直到 time.sleep 代码运行之后，我在 dict_str 中收到此错误。如果我在函数之外声明 msg 并且 msg = None 我没有得到 mydata['lowerpredict'] 和 mydata['Upperpredict']...代码精确错误在 dict_str 中。 有人有解决办法吗？

Answer 1

你需要

1. 在全球范围内声明msg：

msg = None

def on_message(client, userdata, message):
    # ...

    global msg
    msg = str(message.payload)

# ...

client = mqtt.Client("P1")
client.on_message= on_message

# ... 

print(msg)

1. 将访问msg的代码放入函数中：

def on_message(client, userdata, message):
    # ...

    on_message_received(client, userdata, str(message.payload))

def on_message_received(client, userdata, msg):
    print(msg)

    # ...

client = mqtt.Client("P1")
client.on_message= on_message