Return value from thread

How do I get a thread to return a tuple or any value of my choice back to the parent in Python?

I suggest you instantiate a Queue.Queue before starting the thread, and pass it as one of the thread's args: before the thread finishes, it .puts the result on the queue it received as an argument. The parent can .get or .get_nowait it at will.

Queues are generally the best way to arrange thread synchronization and communication in Python: they're intrinsically thread-safe, message-passing vehicles -- the best way to organize multitasking in general!-)

You should pass a Queue instance as a parameter then you should .put() your return object into the queue. You can gather the return value via queue.get() whatever object you put.

Sample:

queue = Queue.Queue()
thread_ = threading.Thread(
                target=target_method,
                name="Thread1",
                args=[params, queue],
                )
thread_.start()
thread_.join()
queue.get()

def target_method(self, params, queue):
 """
 Some operations right here
 """
 your_return = "Whatever your object is"
 queue.put(your_return)

Use for multiple threads:

#Start all threads in thread pool
    for thread in pool:
        thread.start()
        response = queue.get()
        thread_results.append(response)

#Kill all threads
    for thread in pool:
        thread.join()

I use this implementation and it works great for me. I wish you do so.

If you were calling join() to wait for the thread to complete, you could simply attach the result to the Thread instance itself and then retrieve it from the main thread after the join() returns.

On the other hand, you don't tell us how you intend to discover that the thread is done and that the result is available. If you already have a way of doing that, it will probably point you (and us, if you were to tell us) to the best way of getting the results out.

Use lambda to wrap your target thread function and pass its return value back to the parent thread using a queue. (Your original target function remains unchanged without extra queue parameter.)

Sample code:

import threading
import queue
def dosomething(param):
    return param * 2
que = queue.Queue()
thr = threading.Thread(target = lambda q, arg : q.put(dosomething(arg)), args = (que, 2))
thr.start()
thr.join()
while not que.empty():
    print(que.get())

Output:

4

I'm surprised nobody mentioned that you could just pass it a mutable:

>>> thread_return={'success': False}
>>> from threading import Thread
>>> def task(thread_return):
...  thread_return['success'] = True
... 
>>> Thread(target=task, args=(thread_return,)).start()
>>> thread_return
{'success': True}

perhaps this has major issues of which I'm unaware.