twsit文档中的一段代码，其中有个不解之处，请各位大神帮忙解答一下！

我先贴上代码：

from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
from twisted.web import resource, server, static
import cgi

class FingerProtocol(basic.LineReceiver):

    def lineReceived(self, user):
        d = self.factory.getUser(user)

        def onError(err):
            return 'Internal error in server'
        d.addErrback(onError)

        def writeResponse(message):
            self.transport.write(message + '\r\n')
            self.transport.loseConnection()
        d.addCallback(writeResponse)
        
class FingerResource(resource.Resource):

    def __init__(self, users):
        print 'FingerResource is initialized'
        self.users = users
        resource.Resource.__init__(self)

    # we treat the path as the username
    def getChild(self, username, request):
        """
        'username' is a string.
        'request' is a 'twisted.web.server.Request'.
        """
        print self.users
        messagevalue = self.users.get(username)
        username = cgi.escape(username)
        if messagevalue is not None:
           messagevalue = cgi.escape(messagevalue)
           text = '<h1>%s</h1><p>%s</p>' % (username,messagevalue)
        else:
           text = '<h1>%s</h1><p>No such user</p>' % username
        return static.Data(text, 'text/html')

class FingerService(service.Service):

    def __init__(self, filename):
        self.users = {}
        self.filename = filename

    def _read(self):
        for line in file(self.filename):
            user, status = line.split(':', 1)
            user = user.strip()
            status = status.strip()
            self.users[user] = status
        self.call = reactor.callLater(30, self._read)

    def startService(self):
        self._read()
        service.Service.startService(self)

    def stopService(self):
        service.Service.stopService(self)
        self.call.cancel()

    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

    def getFingerFactory(self):
        f = protocol.ServerFactory()
        f.protocol = FingerProtocol
        f.getUser = self.getUser
        return f

    def getResource(self):
        print 'getResource is called.'
        r = FingerResource(self.users)
        return r

application = service.Application('finger', uid=1, gid=1)
f = FingerService('./users')
serviceCollection = service.IServiceCollection(application)
f.setServiceParent(serviceCollection)
internet.TCPServer(79, f.getFingerFactory()
                    ).setServiceParent(serviceCollection)
internet.TCPServer(8000, server.Site(f.getResource())
                    ).setServiceParent(serviceCollection)
                

运行这段代码后，每次我更新users文件的内容以后，getResource返回的FingerResource实例里的users变量是如何被更新的？在这段代码里，我看不到它有被更新！请懂的人帮忙解释一下，谢谢！

---

我已经找到原因了。
users是字典类型，r = FingerResource(self.users)这里传递的是users引用；self.users[user] = status，这里会改变users的内容，所以会看到users每次都有更新。