问null回溯是什么意思？

EN

=========== RESTART: /home/pi/Desktop/Pythonic/Chat/ReadClient.py ===========
Enter name: SuperUser
Enter server port: 5162
> Traceback (most recent call last):

import os, threading
from socket import *



name = input('Enter name: ')

bufsiz = 1024


host = 'localhost'
port = int(input('Enter server port: '))

addr = (host, port)


client = socket(AF_INET , SOCK_STREAM)
##try:
client.connect(addr)
##except socket_error as serr:
##    if serr.errno != errno.ECONNREFUSED:
##        raise serr
##    else:
##        print('Invalid Port number:[111]')
##        port = int(input('Enter server port: '))
##        addr = (host, port)
##        client.connect(addr)

# sending name
client.sendto(name.encode('utf-8'),addr)

os.system('cls' if os.name == 'nt' else 'clear')

def input_loop():
    global data, client
    while True:
        data = input('> ')
        if not data:
            client.sendto('/disconnect'.encode('utf-8'),addr)
            break
        else:
            client.sendto(data.encode('utf-8'),addr)

def recv_loop(client,caddr):
    while True:
        data = client.recv(1024).decode('utf-8')
        if data != 'n_dat':
            if data != '/ping':
                print(data)
            else:
                client.sendto('/ping'.encode('utf-8'),caddr)
                print('pinged by server')

threads = []

dat_thread = threading.Thread(target=input_loop, args=())
dat_thread.start()
thread = threading.Thread(target=recv_loop, args=(client,caddr))
thread.start()

import os, socket, time, threading, random


class Server:


    def __init__(self,host,port,user):
        self.port = port
        self.host = host
        self.user = user
        self.bufsize = 1024
        self.addr = (host,port)

        self.socket = socket.socket(socket.AF_INET , socket.SOCK_STREAM)
        self.socket.bind(self.addr)
        print("Server running on",host,"at port",port)

        self.socket.listen(5)

class rank:

    def __init__(self, level):
        self.level = level

    def getPerms(l):
        return (l==6,l>=6,True,l>=3,l>=2,l>=5,l>=4,l>=3,l>=2,l>=5>l>=6)


    def getPerms(level,action):
        return getperms(level)[action]

    def getLevel(level):
        if(level == 1):
            return 'Guest'
        if(level == 2):
            return 'Experienced'
        if(level == 3):
            return 'Veteran'
        if(level == 4):
            return 'Donor'
        if(level == 5):
            return 'Mod'
        if(level == 6):
            return 'Admin'
        if(level == 7):
            return 'Owner'
        else:
            return False

        # level scale

        # A = Server control
        # B = Ban
        # C = Chat
        # D = Direct Message
        # H = Vanish
        # I = ignore              
        # K = Kick
        # M = Server mute
        # T = Title
        # V = View members
        # U = Unban

##                  A B C D I K M T V H U 
##   _____________________________________
## 1 |    Guest    | | |X| | | | | | | | |
## 2 | Experienced | | |X| |X| | | |X| | |
## 3 |   Veteran   | | |X|X|X| | |X|X| | |
## 4 |    Donor    | | |X|X|X| |X|X|X|X| |
## 5 |     Mod     | | |X|X|X|X|X|X|X|X| |
## 6 |    Admin    | |X|X|X|X|X|X|X|X|X|X|
## 7 |    Owner    |X|X|X|X|X|X|X|X|X|X|X|   
##   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~        



def recv_loop(server,client,caddr):
    print ('Connected To',caddr)

    while True:
        global clients
        global ping_count
        name = clients[client]
        data = client.recv(1024)
        namecheck = getrank(caddr[0],name,)
        formattime = time.strftime(time.strftime("%H:%M:%S",time.gmtime()))
        if not data:
            break
        if data.decode('utf-8') == '/disconnect':
            print(formattime + ' : '  +'[' + namecheck + ']'+ name +' has disconnected ')
            break
        if data.decode('utf-8') == '/ping':
            pings = 0
        mssg = str(formattime + ' : '  +'[' + namecheck + ']'+ name +': '+ data.decode('utf-8'))
        print(formattime + ' : '  +'[' + namecheck + ']'+ name +': '+ data.decode('utf-8'))
        for c in clients:
            if c != client:
                c.send(mssg.encode('utf-8'))
            else:
                c.send(bytes('n_dat','utf-8'))
        log(name, data.decode('utf-8'),getrank(caddr[0],name))
    client.close()


def log(name, msg, rank):
    with open('log.txt', 'a') as log:
        log.write(time.strftime("%Y-%m-%d %H:%M:%S",time.gmtime())+ ' ' + name + ': ' + msg + '\n')

def getrank(ip, name):
    with open('ranks.txt', 'r') as ranks:
        for line in ranks:
            addr = line.split('$',1)[0]
            if addr == ip:
                rank = (line.split('$$',1)[0]).split('$')[1]
                return rank
        print('new user')
        writerank(ip,name)
        return ' Guest '

def writerank(ip,name):
    with open('ranks.txt','a') as file:
        file.write(ip + '$' + ' Guest ' + '$$' + name + '$$$' + '0/n')

def ping(client, ping_rate):
    global ping_count
    while True:
        time.sleep(60/ping_rate)
        client.send(bytes('/ping','utf-8'))
        print('pinging client ' + str(client))
        ping_count = ping_count + 1



##def getname(caddr):
##    with open('ranks.txt', 'r+') as ranks:
##        for line in ranks:
##            addr = line.split(' .R. ')[0]
##            if addr == caddr:
##                name = line.split(' ... ')[1]
##                return bytes(name,'utf-8')       
##

host = 'localhost'
port = random.randint(5000,6000)
user = 'No one'

name = input('Server name : ')
ping_rate = 6

server = Server(host, port, user)

clients = {}
threads = []

ping_count = 0

while True:
    client, caddr = server.socket.accept()
    # name extraction
    name = client.recv(1024)
    #name = getname(caddr)

    clients[client] = name.decode('utf-8')

    pingthread = threading.Thread(target=ping, args=(client,ping_rate))
    thread = threading.Thread(target=recv_loop, args=(server,client, caddr))
    pingthread.start()
    thread.start()