尝试实现扭曲的deferredlist时的奇怪行为 [英] Strange behaviour when trying to implement twisted deferredlist

问题描述

我刚开始尝试构建简单的POC，但是我不断遇到以下错误.

I'm new to twisted and trying to build a simple POC, however I keep getting the following error.

running
[]
running
[]
running
[]
running
[]
running
[]
Traceback (most recent call last):
  File "./poc.py", line 23, in <module>
    dl = defer.DeferredList([tasks])
  File "/usr/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 820, in __init__
    deferred.addCallbacks(self._cbDeferred, self._cbDeferred,
AttributeError: 'list' object has no attribute 'addCallbacks'

我一直在阅读相关的扭曲文档和指南，但似乎无法弄清我做错了什么.有人知道导致此异常的原因吗?

I have been reading through the relevant twisted documentation and guides and can't seem to work out what I'm doing wrong. Does anybody know what is causing this exception?

#!/usr/bin/env python
from twisted.internet import defer

def task_to_run(data):
  print 'running'
  print data

def finished(res):
  print 'finished', res

tasks = []

for x in range(0,5):
  d = defer.Deferred()      
  d.addCallback(task_to_run)
  tasks.append(d)

dl = defer.DeferredList([tasks])
dl.addCallback(finished) 

推荐答案

假设 task_to_run 确实是异步运行的，那么@Elisha就是在指出您的问题(您的示例代码列出了列表，它不应该).因此，可运行的代码如下:

Assuming that task_to_run really is something that is running async, then @Elisha was pointing you at the issue (your example code lists the list and it shouldn't). So runnable code looks like:

#!/usr/bin/env python
from twisted.internet import defer

def task_to_run(data):
  print 'running'
  print data

def finished(res):
  print 'finished', res

tasks = []

for x in range(0,5):
  d = defer.Deferred()      
  d.addCallback(task_to_run)
  d.callback("blah - " + str(x)) # Fire them as I make them
  tasks.append(d)

dl = defer.DeferredList(tasks)

dl.addCallback(finished) 

输出为:

% ./deferredList.py
running
blah - 0
running
blah - 1
running
blah - 2
running
blah - 3
running
blah - 4
finished [(True, None), (True, None), (True, None), (True, None), (True, None)]

关于DeferredLists的非常不错的文档位于:延迟参考

BTW very nice docs on DeferredLists are at: Deferred Reference

但是，如果任务实际上并未异步运行，那么您真的可以只设置一个延迟队列:

But if the tasks aren't actually running async then you really could just make one defer queue:

#!/usr/bin/env python
from twisted.internet import defer

def task_to_run(data):
  print 'running'
  print data
  return data

def finished(res):
  print 'finished', res

d = defer.Deferred()      

for x in range(0,5):
  d.addCallback(task_to_run)

d.addCallback(finished) 

d.callback("blah") # Fire the deferred

运行方式:

% ./deferred.py
running
blah
running
blah
running
blah
running
blah
running
blah
finished blah

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