下面的函数foo返回一个字符串'foo'。我如何才能获得从线程的目标返回的值'foo' ?

from threading import Thread

def foo(bar):
    print('hello {}'.format(bar))
    return 'foo'
    
thread = Thread(target=foo, args=('world!',))
thread.start()
return_value = thread.join()

上面所示的“一种明显的方法”不起作用:thread.join()返回None。


当前回答

GuySoft的想法很棒,但我认为对象不一定要从Thread继承,start()可以从接口中删除:

from threading import Thread
import queue
class ThreadWithReturnValue(object):
    def __init__(self, target=None, args=(), **kwargs):
        self._que = queue.Queue()
        self._t = Thread(target=lambda q,arg1,kwargs1: q.put(target(*arg1, **kwargs1)) ,
                args=(self._que, args, kwargs), )
        self._t.start()

    def join(self):
        self._t.join()
        return self._que.get()


def foo(bar):
    print('hello {0}'.format(bar))
    return "foo"

twrv = ThreadWithReturnValue(target=foo, args=('world!',))

print(twrv.join())   # prints foo

其他回答

我发现做到这一点的最短和最简单的方法是利用Python类及其动态属性。您可以使用threading.current_thread()从派生线程的上下文中检索当前线程,并将返回值赋给一个属性。

import threading

def some_target_function():
    # Your code here.
    threading.current_thread().return_value = "Some return value."

your_thread = threading.Thread(target=some_target_function)
your_thread.start()
your_thread.join()

return_value = your_thread.return_value
print(return_value)

根据上面提到的,下面是适用于Python3的更通用的解决方案。

import threading

class ThreadWithReturnValue(threading.Thread):
    def __init__(self, *init_args, **init_kwargs):
        threading.Thread.__init__(self, *init_args, **init_kwargs)
        self._return = None
    def run(self):
        self._return = self._target(*self._args, **self._kwargs)
    def join(self):
        threading.Thread.join(self)
        return self._return

使用

        th = ThreadWithReturnValue(target=requests.get, args=('http://www.google.com',))
        th.start()
        response = th.join()
        response.status_code  # => 200

最好的方法…定义一个全局变量,然后在线程函数中更改该变量。没有可以传递或取回的东西

from threading import Thread

# global var
radom_global_var = 5

def function():
    global random_global_var
    random_global_var += 1

domath = Thread(target=function)
domath.start()
domath.join()
print(random_global_var)

# result: 6

您可以在线程函数的作用域之上定义一个可变变量,并将结果添加到该变量中。(我还修改了代码,使其与python3兼容)

returns = {}
def foo(bar):
    print('hello {0}'.format(bar))
    returns[bar] = 'foo'

from threading import Thread
t = Thread(target=foo, args=('world!',))
t.start()
t.join()
print(returns)

返回{'world!”:“foo”}

如果使用函数input作为结果字典的键,则保证每个惟一的输入都在结果中给出一个条目

我对这个问题的解决方案是将函数和线程包装在一个类中。不需要使用池、队列或c类型变量传递。它也是非阻塞的。而是检查状态。参见代码末尾如何使用它的示例。

import threading

class ThreadWorker():
    '''
    The basic idea is given a function create an object.
    The object can then run the function in a thread.
    It provides a wrapper to start it,check its status,and get data out the function.
    '''
    def __init__(self,func):
        self.thread = None
        self.data = None
        self.func = self.save_data(func)

    def save_data(self,func):
        '''modify function to save its returned data'''
        def new_func(*args, **kwargs):
            self.data=func(*args, **kwargs)

        return new_func

    def start(self,params):
        self.data = None
        if self.thread is not None:
            if self.thread.isAlive():
                return 'running' #could raise exception here

        #unless thread exists and is alive start or restart it
        self.thread = threading.Thread(target=self.func,args=params)
        self.thread.start()
        return 'started'

    def status(self):
        if self.thread is None:
            return 'not_started'
        else:
            if self.thread.isAlive():
                return 'running'
            else:
                return 'finished'

    def get_results(self):
        if self.thread is None:
            return 'not_started' #could return exception
        else:
            if self.thread.isAlive():
                return 'running'
            else:
                return self.data

def add(x,y):
    return x +y

add_worker = ThreadWorker(add)
print add_worker.start((1,2,))
print add_worker.status()
print add_worker.get_results()