我正在使用MQTT订阅主题并接收消息。到目前为止我已经编写了这个代码并且它可以正常订阅，但我确定了解析从MQTT代理接收的有效负载的方法时遇到了问题。我一直试图获得我在有效载荷中看到的数值，但我无法找到解析这些数据的正确方法。有什么想法/建议吗？谢谢！
有更多不相关的代码。这只是一个片段。
import paho.mqtt.client as mqtt
import json
#Call back functions
# gives connection message
def on_connect(client,userdata,rc):
print("Connected with result code:"+str(rc))
# subscribe for all devices of user
client.subscribe('+/devices/+/up')
def on_connect(client,userdata,rc):
print("Connected with result code:"+str(rc))
# subscribe for all devices of user
client.subscribe('+/devices/+/up')
def on_message(client,userdata,msg):
print"Topic",msg.topic + "\nMessage:" + str(msg.payload)
node_data = str(msg.payload)
print '\r\n test'
print node_data
j = json.loads(node_data)
print "\r\n after loads: "
print j
我的输出：
Message:{"payload":"Dgv+CggGBCYFAPMLAgc=","fields":{"Light":58.32,"Pressure":98569.5,"Temp":32.4375,"X_accel":0.6875,"Y_accel":-0.125,"Z_accel":0.625},"port":1,"counter":8,"dev_eui":"000000007D9050C1","metadata":[{"frequency":904.3,"datarate":"SF7BW125","codingrate":"4/5","gateway_timestamp":2090979635,"gateway_time":"2016-07-28T02:26:15.386371Z","channel":2,"server_time":"2016-07-28T02:06:13.075194806Z","rssi":-13,"lsnr":9.5,"rfchain":0,"crc":1,"modulation":"LORA","gateway_eui":"0080000000009BE6","altitude":911,"longitude":-93.19677,"latitude":45.10303}]}
test
{"payload":"Dgv+CggGBCYFAPMLAgc=","fields":{"Light":58.32,"Pressure":98569.5,"Temp":32.4375,"X_accel":0.6875,"Y_accel":-0.125,"Z_accel":0.625},"port":1,"counter":8,"dev_eui":"000000007D9050C1","metadata":[{"frequency":904.3,"datarate":"SF7BW125","codingrate":"4/5","gateway_timestamp":2090979635,"gateway_time":"2016-07-28T02:26:15.386371Z","channel":2,"server_time":"2016-07-28T02:06:13.075194806Z","rssi":-13,"lsnr":9.5,"rfchain":0,"crc":1,"modulation":"LORA","gateway_eui":"0080000000009BE6","altitude":911,"longitude":-93.19677,"latitude":45.10303}]}
after loads:
{u'fields': {u'Y_accel': -0.125, u'Temp': 32.4375, u'X_accel': 0.6875, u'Light': 58.32, u'Pressure': 98569.5, u'Z_accel': 0.625}, u'counter': 8, u'port': 1, u'dev_eui': u'000000007D9050C1', u'payload': u'Dgv+CggGBCYFAPMLAgc=', u'metadata': [{u'gateway_time': u'2016-07-28T02:26:15.386371Z', u'server_time': u'2016-07-28T02:06:13.075194806Z', u'datarate': u'SF7BW125', u'gateway_eui': u'0080000000009BE6', u'modulation': u'LORA', u'gateway_timestamp': 2090979635, u'longitude': -93.19677, u'crc': 1, u'frequency': 904.3, u'rfchain': 0, u'codingrate': u'4/5', u'lsnr': 9.5, u'latitude': 45.10303, u'rssi': -13, u'altitude': 911, u'channel': 2}]}
我希望能够从这个...字符串中提取数值？Dict？Json？（有效载荷）用于＆＃39; Temp＆＃39;＆＃39; Light＆＃39;，＆＃39 ;压力＆＃39;等...参数。非常感谢任何建议。＆＃39; 我尝试了以下但我收到此错误。不会告诉我太多......
data = json.loads(node_data)
Press = data['Pressure']
print Press
文件＆＃34; C：\ Python27 \ My_Py_27_Codes \ scratch_py_mqtt.py＆＃34;，第25行，在on_message中 按=数据[＆＃39;压力＆＃39;]
KeyError: 'Pressure'
显然＆＃39;压力＆＃39;这本词典不是关键吗？
答案 0 :(得分：2)
node_data = {"payload":"dsgsg","fields":{"pressure":34,"temp":35}}
data = json.loads(node_data)
Press = data['fields']['Pressure']
print Press
您必须提供提交的确切位置。在您的情况下，pressure位于fields字典
答案 1 :(得分：0)
所以经过几个小时的挠头和编码后＃39;走了，我设法实现了我的目标。我不确定它是否是最漂亮的＆＃39;方式或者它是否是最好的方式，但这是我想到的：我正在处理一个＆＃39;词典＆＃39;我必须选择适当的键名字段＆＃39;。这将使我能够获得＆＃39;与＆＃39;字段内的参数（温度，压力，光等）相关的数值。字典的一部分。
def on_message(client,userdata,msg):
print"Topic",msg.topic + "\n\nMessage:" + str(msg.payload)
node_data = str(msg.payload)
print ' \n Sensor Values \r'
my_dict = json.loads(node_data)
params = my_dict.get("fields",None)
light = params.get('Light')
pressure = params.get('Pressure')
temp = params.get('Temp')
x = params.get('X_accel')
y = params.get('Y_accel')
z = params.get('Z_accel')
print ''
print 'Light:' + str(light)
print 'Pressure:' + str(pressure)
print 'Temperature:' + str(temp)
print 'X-accel:' + str(x)
print 'Y-accel:' + str(y)
print 'Z-accel:' + str(z)
print '\n\n'