python多处理中的字符串参数 [英] String arguments in python multiprocessing

问题描述

我正在尝试将字符串参数传递给进程中的目标函数.某种程度上，字符串被解释为包含字符的参数列表.

I'm trying to pass a string argument to a target function in a process. Somehow, the string is interpreted as a list of as many arguments as there are characters.

这是代码:

import multiprocessing

def write(s):
   print s

write('hello')

p = multiprocessing.Process(target=write, args=('hello'))

p.start()

我得到以下输出:

hello
Process Process-1:
Traceback (most recent call last):
>>>   File "/usr/local/lib/python2.5/site-packages/multiprocessing/process.py", line 237, in _bootstrap
    self.run()
  File "/usr/local/lib/python2.5/site-packages/multiprocessing/process.py", line 93, in run
    self._target(*self._args, **self._kwargs)
TypeError: write() takes exactly 1 argument (5 given)

>>>

我做错了什么?我应该如何传递细绳呢?

What am I doing wrong? How am I supposed to pass a stringn?

谢谢Ariel

推荐答案

这是Python中的常见陷阱-如果您想要一个只有一个元素的元组，则需要指定它实际上是一个元组(而不仅仅是带有方括号的东西)-通过在元素后添加逗号来完成.

This is a common gotcha in Python - if you want to have a tuple with only one element, you need to specify that it's actually a tuple (and not just something with brackets around it) - this is done by adding a comma after the element.

要解决此问题，只需在字符串后的方括号内添加逗号:

To fix this, just put a comma after the string, inside the brackets:

p = multiprocessing.Process(target=write, args=('hello',))

这样，Python将按预期将其识别为具有单个元素的元组.目前，Python将您的代码解释为一个字符串.但是，它以这种特定方式失败了，因为字符串实际上是字符列表.因此，Python认为您希望通过("h"，"e"，"l"，"l"，"o").这就是为什么它说您给了我5个参数".

That way, Python will recognise it as a tuple with a single element, as intended. Currently, Python is interpreting your code as just a string. However, it's failing in this particular way because a string is effectively list of characters. So Python is thinking that you want to pass ('h', 'e', 'l', 'l', 'o'). That's why it's saying "you gave me 5 parameters".

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