Question

我正在学习Python并且目前专注于Twisted ......我正在进行一个教程练习，但我似乎无法理解为什么在此代码的第二个版本中修改会导致＆＃ 39;计数＆＃39;在反应堆启动之前执行的功能。所有改变的都是添加＆＃39;函数的论证。

工作：

class Countdown(object):

counter = 5

def count(self):
    if self.counter == 0:
        reactor.stop()
    else:
        print self.counter, '...'
        self.counter -= 1
        reactor.callLater(1, self.count)

from twisted.internet import reactor

reactor.callWhenRunning(Countdown().count)

print 'Start!'
reactor.run()
print 'Stop!'

破：

class Countdown(object):

counter = 5

def count(self,s):
    if self.counter == 0:
        reactor.stop()
    else:
        print self.counter, '...'
        self.counter -= 1
        reactor.callLater(1, self.count(1))

from twisted.internet import reactor

reactor.callWhenRunning(Countdown().count(1))

print 'Start!'
reactor.run()
print 'Stop!'

这里是追溯：

Traceback (most recent call last):
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 15, in <module>
    reactor.callWhenRunning(Countdown().count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 11, in count
    reactor.callLater(1, self.count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 11, in count
    reactor.callLater(1, self.count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 11, in count
    reactor.callLater(1, self.count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 11, in count
    reactor.callLater(1, self.count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 11, in count
    reactor.callLater(1, self.count(1))
  File "C:\Python27\twistedexample\basic-twisted\countdown.py", line 7, in count
    reactor.stop()
  File "C:\Python27\lib\site-packages\twisted\internet\base.py", line 580, in stop
  "Can't stop reactor that isn't running.")
  ReactorNotRunning: Can't stop reactor that isn't running.

对此的任何意见表示赞赏，我觉得我在这里遗漏了一些重要内容并且不想跳过它。

Answer 1

代码的第一个版本传递对函数count的引用（以便以后可以调用它），而代码的破坏版本传递结果 count(1)的函数调用，它将是None（因为count没有return值）。所以你基本上做了什么改变了这个：

reactor.callWhenRunning(Countdown().count)

到此：

reactor.callWhenRunning(None)

最重要的是，你立即调用count(1)而不是注册它以便以后调用！这解释了您看到的错误，因为在您到达第reactor.run()行之前倒计时正在运行。

这同样适用于调用reactor.callLater(1, self.count(1))的行count(1)，可能返回None，而实际上并未使用callLater注册任何函数。

python / twisted - 这段代码有什么问题？

1 个答案: