下面的函数foo返回字符串'foo'.如何获取线程目标返回的值'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()
上面显示的"一个显而易见的方法"是行不通的:thread.join()返回None.
在Python 3.2+中，stdlib concurrent.futures模块为threading提供了更高级别的API，包括将工作线程的返回值或异常传递回主线程:
import concurrent.futures
def foo(bar):
print('hello {}'.format(bar))
return 'foo'
with concurrent.futures.ThreadPoolExecutor() as executor:
future = executor.submit(foo, 'world!')
return_value = future.result()
print(return_value)