python - 尝试实现扭曲延迟列表时的奇怪行为

Question

我是 twisted 的新手，正在尝试构建一个简单的 POC，但是我不断收到以下错误。

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，但似乎无法弄清楚我做错了什么。有谁知道是什么导致了这个异常？

#!/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) 

Answer 1

假设 task_to_run 确实是异步运行的，那么@Elisha 指出了您的问题(您的示例代码列出了列表，但它不应该)。所以可运行的代码看起来像:

#!/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)]

顺便说一下，关于 DeferredLists 的非常好的文档位于:Deferred Reference

---

但是如果任务实际上不是异步运行的，那么你真的可以只创建一个延迟队列:

#!/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