sleepnir sleepnir - 5 months ago 39
Python Question

Assigning return value of function to a variable, with multiprocessing? And a problem about IDLE?

I'm trying to understand multiprocessing in python.

from multiprocessing import Process

def multiply(a,b):
print(a*b)
return a*b

if __name__ == '__main__':
p = Process(target= multiply, args= (5,4))
p.start()
p.join()
print("ok.")


In this codeblock, for example, if there was an variable that called "result". How can we assign return value of multiply function to "result"?

And a little problem about IDLE: when i'm tried to run this sample with Python Shell, it doesn't work properly? If i double click .py file, output is like that:

20
ok.


But if i try to run this in IDLE:

ok.


Thanks...

Answer

Ok, i somehow managed this. I looked to python documentation, and i learnt that: with using Queue class, we can get return values from a function. And final version of my code is like this:

from multiprocessing import Process, Queue

def multiply(a,b,que): #add a argument to function for assigning a queue
    que.put(a*b) #we're putting return value into queue

if __name__ == '__main__':
    queue1 = Queue() #create a queue object
    p = Process(target= multiply, args= (5,4,queue1)) #we're setting 3rd argument to queue1
    p.start()
    print(queue1.get()) #and we're getting return value: 20
    p.join()
    print("ok.")

And there is also a pipe() function, i think we can use pipe function,too. But queue worked for me, now.