twisted defer 使 class 实例变量的赋值无效

Question

我有一个 class A 有两个方法， method_one 使用延迟和 method_two ，在回调函数中我将值设置为 self.value 并添加它延迟的回调链。但在那之后 self.value 仍然是 method_two 中的原始值。总之回调函数中self.value的赋值是无效的

from twisted.internet import utils, reactor
class A(object):

    def __init__(self):
        self.value = []

    def method_one(self):
        d = utils.getProcessOutput('/bin/sh', ('-c', 'ls /home')) # return a defer
        def set_self_value(result):
            self.value = result.split()  # assign result.split() to self.value
        d.addCallback(set_self_value)

    def method_two(self):
        print self.value  # it is still [] rather than result

a = A()
a.method_one()
a.method_two()
reactor.run()

output:
[]  # i expect self.value is ['lost+found', 'user']
lost+found
user

提前致谢:-)

Answer 1

问题是，由于 method_one 被推迟，所以，它没有立即调用 set_self_value，而是先进入下一步 a.method_two()，因此与当时一样该值尚未设置，您会得到一个空列表。

要确保 method_two 在 method_one 之后调用，请将其添加到回调链中：

import twisted
from twisted.internet import utils
from twisted.internet import reactor


class A(object):

    def __init__(self):
        self.value = []

    def method_one(self):
        d = utils.getProcessOutput('/bin/sh', ('-c', 'ls /home'))
        def set_self_value(result):
            print 'called set'
            self.value = 100
        d.addCallback(set_self_value)
        d.addCallback(self.method_two)

    def method_two(self, *args): # *args required to handle the result
        print 'called two'
        print self.value

def main():
    a = A()
    a.method_one()


reactor.callWhenRunning(main)
reactor.run()

输出：

called set
called two
100

twisted defer 使 class 实例变量的赋值无效

twisted defer make the assignment of class instance variables is invalid

python

twisted

twisted.internet