如何選擇附加列表？

Question

我正在通過RFID閱讀器收到我的消息。我所試圖做的是消除重複和只添加到列表以下兩個條件：

1. 如果他們的ID（epc在這種情況下）是獨一無二的，（完成）

2. 的datetime （每5分鐘，所以我可以跟蹤相同的標籤仍然是由RFID閱讀器讀取）是間隔5分鐘後

   import paho.mqtt.client as mqtt 
   import json 
   
   testlist = []  
   
   def on_message(client, userdata, msg): 
       payloadjson = json.loads(msg.payload.decode('utf-8')) 
       line = payloadjson["value"].split(',') 
       epc = line[1] 
       datetime = payloadjson['datetime'] 
       # datetime is in this string format '2016-04-06 03:21:17' 
   
       payload = {'datetime': datetime, 'epc': epc[11:35]} 
   
       # this if-statement satisfy condition 1 
       if payload not in testlist: 
        testlist.append(payload) 
        for each in teslist: 
         print (each) 
   
   test = mqtt.Client(protocol = mqtt.MQTTv31) 
   test.connect(host=_host, port=1883, keepalive=60, bind_address="") 
   test.on_connect = on_connect 
   test.on_message = on_message 
   test.loop_forever() 
   

我怎麼能達到條件2？

UPDATE
我的目標不明確道歉，我試圖實現

我希望的輸出是這個樣子：

{'datetime': 2016-04-06 03:21:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:21:18', 'epc': 00000002} # from Tag B 
... 
... 
# 5 minutes later 
{'datetime': 2016-04-06 03:21:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:21:18', 'epc': 00000002} # from Tag B 
{'datetime': 2016-04-06 03:26:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:26:18', 'epc': 00000002} # from Tag B 
... 
... 
# Another 5 minutes later 
{'datetime': 2016-04-06 03:21:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:21:18', 'epc': 00000002} # from Tag B 
{'datetime': 2016-04-06 03:26:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:26:18', 'epc': 00000002} # from Tag B 
{'datetime': 2016-04-06 03:31:17', 'epc': 00000001} # from Tag A 
{'datetime': 2016-04-06 03:31:18', 'epc': 00000002} # from Tag B 
... 
... 

Answer 1

你的問題有點不清楚。假設您想要更新testlist，如果它是新的epc，或者自上次更新epc以來已經超過5分鐘。在這種情況下，dict()可以很好地工作。使用標準庫中的datetime模塊計算日期或時間的差異。

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

TIMELIMIT = dt.timedelta(minutes=5) 

testlist = {}  ## <<-- changed this to a dict() 

def on_message(client, userdata, msg): 
    payloadjson = json.loads(msg.payload.decode('utf-8')) 
    line = payloadjson["value"].split(',') 
    epc = line[1] 

    # this converts the time stamp string to something python can 
    # use in date/time calculations 
    when = dt.datetime.strptime(payloadjson['datetime'], '%Y-%m-%d %H:%M:%S') 

    if epc not in testlist or when - testlist[epc] > TIMELIMIT: 
     testlist[epc] = when 

     for epc, when in teslist.items(): 
      print (epc, when) 

Answer 2

這可能是一個更簡單方法：

class EPC(object): 
    def __init__(self, epc, date): 
     self.epc = epc 
     self.datetime = date 
    def __eq__(self, other): 
     difference = datetime.strptime(self.datetime, '%Y-%m-%d %H:%M:%S') - datetime.strptime(other.datetime, '%Y-%m-%d %H:%M:%S') 
     return self.epc == other.epc and timedelta(minutes=-5) < difference < timedelta(minutes=5) 
    def __ne__(self, other): 
     difference = datetime.strptime(self.datetime, '%Y-%m-%d %H:%M:%S') - datetime.strptime(other.datetime, '%Y-%m-%d %H:%M:%S') 
     return self.epc != other.epc or (self.epc == other.epc and (difference > timedelta(minutes=5) or difference < timedelta(minutes=-5))) 

payload = EPC(date, epc[11:35]) 
if payload not in test_list: 
    test_list.append(payload) 

Answer 3

我不知道epc值是否可以來回切換。也就是說，是否可能出現epc值'A'，然後epc值'B'，然後epc值'A'再次出現？ （也可能是A，B，C，等等？）

如果假設是隻會有一個標籤，那麼只要看看最近的條目：

last_tag = testlist[-1] 
last_dt = last_tag['datetime'] 

現在你可以比較一下目前datetime與以前的值，看看它是否適合你的窗口。

請注意，由於日期時間不斷變化，因此將日期時間代碼放入has中並不適用於您的現有代碼，因此payload not in testlist將始終爲真，除非您獲得兩個完全相同的RFID讀數第二。

Answer 4

有解決你的問題有幾點：

1. 對於ID唯一性，你需要檢查的epc場而已，而不是整個​​對象，因爲​​對象包括datetime。您可以使用set來存儲所有看到的ID。
2. 的時間檢測，使用datetime和timedelta要比較的對象時

# -*- coding: utf-8 -*- 
""" 
06 Apr 2016 
To answer http://stackoverflow.com/questions/36440618/ 
""" 

# Import statements 

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

testlist = [] 
seen_ids = set() # The set of seen IDs 
five_minutes = dt.timedelta(minutes=5) # The five minutes differences 

def on_message(client, userdata, msg): 
    payloadjson = json.loads(msg.payload.decode('utf-8')) 
    line = payloadjson["value"].split(',') 
    epc = line[1] 
    datetime = payloadjson['datetime'] 
    # datetime is in this string format '2016-04-06 03:21:17' 

    # Convert the string into datetime object 
    datetime = dt.datetime.strptime(datetime, '%Y-%m-%d %H:%M:%S') 

    payload = {'datetime': datetime, 'epc': epc[11:35]} 

    # this if-statement satisfy condition 1 
    if payload['epc'] not in seen_ids: # Need to use another set 
     should_add = True    # The flag whether to add 
     if len(testlist) > 0: 
      last_payload = testlist[-1] 
      diff = payload['datetime'] - last_payload['datetime'] 
      if diff < five_minutes:  # If the newer one is less than five minutes, do not add 
       should_add = False 
     if should_add: 
      seen_ids.add(payload['epc']) # Mark as seen 
      testlist.append(payload) 
      print ('Content of testlist now:') 
      for each in testlist: 
       print (each) 

class Message(object): 
    def __init__(self, payload): 
     self.payload = payload 

def main(): 
    test_cases = [] 
    for i in range(10): 
     payload = '{{"value":",{}","datetime":"2016-04-06 03:{:02d}:17"}}'.format('0'*34+str(i), i) 
     test_case = Message(payload) 
     test_cases.append(test_case) 
    for test_case in test_cases: 
     on_message(None, None, test_case) 

if __name__ == '__main__': 
    main() 

會打印：

 
Content of testlist now: 
{'epc': u'000000000000000000000000', 'datetime': datetime.datetime(2016, 4, 6, 3, 0, 17)} 
Content of testlist now: 
{'epc': u'000000000000000000000000', 'datetime': datetime.datetime(2016, 4, 6, 3, 0, 17)} 
{'epc': u'000000000000000000000005', 'datetime': datetime.datetime(2016, 4, 6, 3, 5, 17)}