Concurrently run two functions that take parameters and return lists?

Question

I understand that two functions can run in parallel using multiprocessing or threading modules, e.g. Make 2 functions run at the same time and Python m

Answer 1

Thread's target function cannot return a value. Or, I should say, the return value is ignored and as such, not communicated back to spawning thread. But here's a couple things you can do:

1) Communicate back to spawning thread using Queue.Queue. Note the wrapper around the original functions:

from threading import Thread
from Queue import Queue

def func1(x):
    return [i*i for i in x]

def func2(x):
    return [i*i*i for i in x]

nums = [1,2,3,4,5]

def wrapper(func, arg, queue):
    queue.put(func(arg))

q1, q2 = Queue(), Queue()
Thread(target=wrapper, args=(func1, nums, q1)).start() 
Thread(target=wrapper, args=(func2, nums, q2)).start() 

print q1.get(), q2.get()

2) Use global to access result lists in your threads, as well as the spawning process:

from threading import Thread

list1=list()
list2=list()

def func1(x):
    global list1
    list1 = [i*i for i in x]

def func2(x):
    global list2
    list2 = [i*i*i for i in x]

nums = [1,2,3,4,5]

Thread(target = func1, args=(nums,)).start()
Thread(target = func2, args=(nums,)).start()

print list1, list2