How can I use COM and multiprocessing at the same time in Python?

Question

I'm trying to make two processes and make them communicate to each other. One of them gets values through a COM library using win32com, and the other just gets the values from the first process via a queue and prints them out. I think the code below has no problem, but it doesn't work(p2 process doesn't show values at all). If I just make the first process print queue values in the same process by

item = self.q.get()
print(item)

it shows values in the queue. So, I think putting values in the queue has no problem, and therefore, there could be some problems in exchanging values via the queue, using win32com

import win32com.client
import os
import multiprocessing as mp
from PyQt4.QtGui import QApplication
from datetime import datetime, timedelta

global q
q = mp.Queue()          # A queue is used to send values from p1 to p2                                                        

class RealTrEventHandler(object):          
    def __init__(self):
        self.q = q                                                            

    def OnReceiveRealData(self,szTrCode):
        date = datetime.utcnow() + timedelta(hours=3)
        type = self.GetFieldData("OutBlock", "cgubun")

        appending_line = date + ', ' + type

        self.q.put(appending_line)
        #item = self.q.get()                     # it prints values out if these are not comments
        #print(item)

def ticker():
    loop = QApplication([])
    global instXASession, instXAReal
    print('TICKER: ', os.getpid() )

    # When an event occurs, it calls RealTrEventHandler class
    instXAReal = win32com.client.DispatchWithEvents("XA_DataSet.XAReal", RealTrEventHandler) 
    instXAReal.LoadFromResFile("C:\\eBEST\\xingAPI\\Res\\OVC.res")
    instXAReal.SetFieldData("InBlock", "symbol", "CLX17")

    loop.exec_() 

class listener(mp.Process):           # What listener does is only to get values via the queue and prints them out 
    def __init__(self):
        mp.Process.__init__(self)
        self.q = q

    def run(self):
        print('CSM PID: ', os.getpid() )
        while True:
            item = self.q.get()
            print(item)

if __name__ == '__main__':
    loop = QApplication([])     

    print('MAIN: ', os.getpid() )
    p1 = mp.Process( target = ticker, args=() )
    p1.start()

    p2 = listener()
    p2.start()

    mp.freeze_support()

    loop.exec_()                

Could anyone give me some advice?

Answer 1

Have you tried to explicitly declare q as global in your listener and RealTrEventHandler class? E.g.:

class listener(mp.Process):
    global q
    def __init__(self):
        mp.Process.__init__(self)
        self.q=q

Another way of passing variables between (at least) threads is using the buildins-module, but I'm not sure if multiprocessing is so much different.