python/twisted这段代码有什么问题？

Question

我正在学习Python，目前正在关注Twisted……我正在做一个教程练习，但是我似乎不明白为什么第二个版本的代码修改会导致“count”函数在反应堆启动之前执行。所做的更改只是将“s”参数添加到函数中。在

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!'

破损：

^{pr2}$

回溯如下：

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.

我很感激你在这方面的任何意见，我觉得我遗漏了一些重要的东西，我不想跳过它。在

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），而断开的代码版本传递count(1)函数调用的结果，这将是None（因为count没有return值）。所以你所做的基本改变是：

reactor.callWhenRunning(Countdown().count)

为此：

^{pr2}$

除此之外，您还可以立即调用count(1)，而不是为以后的调用注册它！这解释了您看到的错误，因为在到达reactor.run()行之前倒计时正在运行。在

这同样适用于reactor.callLater(1, self.count(1))行，它调用count(1)，可能返回None，实际上没有向{}注册任何函数。在