如何在Python中实现实时跟踪机制？

我想实现一种“第一次看到”和“最后一次看到”的方式来跟踪来自RFID阅读器的消息

下面的代码管理跟踪每个唯一的消息，并每5分钟更新一次

import paho.mqtt.client as mqtt
import json
import datetime as dt

time_interval = dt.timedelta(minutes=5)

dic1 = {}
update = []   

def on_message(client, userdata, msg):
    payloadjson = json.loads(msg.payload.decode('utf-8'))
    line = payloadjson["value"].split(',')
    epc =  line[1]
    rfid_input = "EPC_NO.: " + epc[11:35]
    when = dt.datetime.strptime(datetime, '%Y-%m-%d %H:%M:%S')


    if rfid_input not in dic1 or (when - dic1[rfid_input] > time_interval):
        dic1[rfid_input] = when
        update.append(dic1)
        for key, value in update[-1].items():
            print (key, value)
        print ()

我如何记录“第一次看到”的日期和时间并打印出来

比如：

# At the very beginning
EPC_NO.: 012345  FIRST SEEN AT 2016-04-18 08:59:33    LAST SEEN AT 2016-04-18 08:59:33
EPC_NO.: 056789  FIRST SEEN AT 2016-04-18 09:00:23    LAST SEEN AT 2016-04-18 09:00:23

# 5 mins later
EPC_NO.: 012345  FIRST SEEN AT 2016-04-18 08:59:33    LAST SEEN AT 2016-04-18 09:04:33
EPC_NO.: 056789  FIRST SEEN AT 2016-04-18 09:00:23    LAST SEEN AT 2016-04-18 09:05:23

# 10 mins later **(EPC_NO.: 056789 is not read)
EPC_NO.: 012345  FIRST SEEN AT 2016-04-18 08:59:33    LAST SEEN AT 2016-04-18 09:09:33
EPC_NO.: 056789  FIRST SEEN AT 2016-04-18 09:00:23    LAST SEEN AT 2016-04-18 09:05:23

---

我将使用一个类来收集您需要的所有信息：

import paho.mqtt.client as mqtt
import json
import datetime as dt

time_interval = dt.timedelta(minutes=5)

dic1 = {}


class EPC():
    def __init__(self,when):
        self.first_seen = when
        self.last_print = when
        self.last_seen = when

def on_message(client, userdata, msg):
    payloadjson = json.loads(msg.payload.decode('utf-8'))
    line = payloadjson["value"].split(',')
    epc =  line[1]
    rfid_input = "EPC_NO.: " + epc[11:35]
    when = dt.datetime.today()

    if rfid_input not in dic1:
        dic1[rfid_input] = EPC(when)
        print_all = True

    else:
        dic1[rfid_input].last_seen = when
        print_all = when-dic1[rfid_input].last_print > time_interval

    if print_all:
        for (key, value) in dic1.items():
            first_str = "%04d-%02d-%02d %02d:%02d:%02d"%(value.first_seen.year,value.first_seen.month,value.first_seen.day,value.first_seen.hour,value.first_seen.minute,value.first_seen.second)
            last_str = "%04d-%02d-%02d %02d:%02d:%02d"%(value.last_seen.year,value.last_seen.month,value.last_seen.day,value.last_seen.hour,value.last_seen.minute,value.last_seen.second)

            print "EPC_NO.: %06d    FIRST SEEN AT %s    LAST SEEN AT %s"%(key, first_str,last_str)
            value.last_print = when

---

我无法测试，请告诉我是否有问题。

谢谢您的时间@Vince！我刚刚尝试了您的解决方案，我看到

print\u all=when-testlist[rfid\u input]。上次打印>时间间隔//类型错误：不支持的操作数类型为-：'str'和'str'

。有没有更好的方法来处理数据类型？我认为最好将

when

作为

datetime.datetime

对象来维护。提供更多的灵活性。是的，你是完全正确的。现在应该好多了。