3

我有一个类 A 有两个方法,method_one 使用 defer 和 method_two ,在回调函数中我为 self.value 设置了一个值并将其添加到 defer 的回调链中。但之后 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 :-)

4

1 回答 1

3

问题是,由于method_one被推迟了,所以它不是set_self_value立即调用,而是首先进入下一步a.method_two(),因此当时尚未设置值,您会得到一个空列表。

确保在将其添加到回调链method_two后调用:method_one

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
于 2015-03-19T19:01:16.107 回答