Issue 36717: Allow retrieval of return value from the target of a threading.Thread (original) (raw)

It would be nice if, after a threading.Thread has completed its run, it were possible to retrieve the return value of the target function. You can do this currently by setting a variable from your target or by subclassing Thread, but this should really be built in. My suggested changes:

• Add an attribute to Thread, retval, initially set to None, that contains the return value of the target after a successful completion.
• Thread.run() should set self.retval to the return value of the target upon completion, and also return this value.
• Thread.join() should return self.retval after a successful completion.

If you're not using Thread.join(), you can directly access Thread.retval to get the return result after a successful run. Thread.run() and Thread.join() both return None in all cases now, so I think a change in their return value would have minimal if any effect on existing code.

Storing the result of Thread.run() can keep Python objects alive longer than expected and it may require a lock on it. I don't think that the additional complexity is worth it. I suggest to reorganize your code to pass the result differently to the caller thread. You can use a queue, a variable, whatever works.