Develop Reference

How i get function outputs from multiprocessing in python?

I have two functions and needed the return values to proceed with the further part of the script...but currently my code giving only the output of the first function...
import multiprocessing
def gm(name):
h = "Good Morning"+str(name)
qout.put(h)
def sal(name):
k="Hi "+str(name)
qout.put(k)
if __name__ == '__main__':
qout = multiprocessing.Queue()
p1 = multiprocessing.Process(target=gm, args=("ashin",))
p2 = multiprocessing.Process(target=sal, args=("ashin",))
p1.start()
p2.start()
p1.join()
p2.join()
result = qout.get()
#output - "Good Morning ashin"
#required output - "Good Morning ashin" & "Hi ashin"
Appreciate your help......

qout.get() gets you the first element from queue. I do not know the bigger picture of what you're are trying to achieve, but you can get all elements from queue like in the following.
from multiprocessing import Process, Queue
def gm(name):
h = "Good Morning"+str(name)
qout.put(h)
def sal(name):
k="Hi "+str(name)
qout.put(k)
if __name__ == '__main__':
qout = Queue()
p1 = Process(target=gm, args=("ashin",))
p2 = Process(target=sal, args=("ashin",))
p1.start()
p2.start()
p1.join()
p2.join()
list1 = []
while not qout.empty():
list1.append(qout.get())
temp = list(map(str, list1))
print(" & ".join(temp))
output
Hi ashin & Good Morningashin

Instead of managing your own output queue, just use the latest Python 3 concurrency features:
from concurrent.futures import as_completed, ProcessPoolExecutor
def gm(name):
return f'Good Morning {name}'
def sal(name):
return f'Hi {name}'
if __name__ == '__main__':
with ProcessPoolExecutor() as exe:
futures = [exe.submit(x, 'ashin') for x in (gm, sal)]
for future in as_completed(futures):
print(future.result())

How to update a dictionary in a while loop?

I am using two loops and cannot figure out how to properly update the dictionary in one loop and use it in the other loop.
In the first loop I am adding a new pair to the dictionary, but in the second loop I don't see any changes, how do I do it correctly?
import time
from multiprocessing import Process
dict_1 = {1:'1'}
def func_1():
while True:
dict_1.update({2:'2'})
print('Result func_1-',dict_1)
time.sleep(5)
def func_2():
while True:
print('Result func_2-',dict_1)
time.sleep(5)
if __name__ == '__main__':
p1 = Process(target=func_1)
p2 = Process(target=func_2)
p1.start()
p2.start()
p1.join()
p2.join()
Result func_1- {1: '1', 2: '2'} Result func_2- {1: '1'}
In the first cycle I see a new pair, but I do not see it in the second cycle.

You can solve this by using multiprocessing.Manager to create a managed dictionary for your purpose this way:
import time
from multiprocessing import Process, Manager
manager = Manager()
dict_1 = manager.dict({1:'1'})
def func_1():
while True:
dict_1.update({2:'2'})
print('Result func_1-',dict_1)
time.sleep(5)
def func_2():
while True:
print('Result func_2-',dict_1)
time.sleep(5)
if __name__ == '__main__':
p1 = Process(target=func_1)
p2 = Process(target=func_2)
p1.start()
p2.start()
p1.join()
p2.join()

'NoneType' object has no attribute '_registry' - Python multiprocessing

I'm using Python multiprocessing Process, Manager (dict). I want to run this script:
from time import sleep
from multiprocessing import Process
from multiprocessing import Queue, Value, Array
from multiprocessing import Manager
def main(id_, graf_dict):
print('Граф {} готов'.format(id_))
graf_dict[id_] = 1
if id_ == '3':
graf_dict[id_] = 0
print(graf_dict)
while True:
check = 0
for key in graf_dict:
if graf_dict[key] == 0:
check = 1
break
if check == 0:
print('Все графы авторизованы')
break
if __name__ == "__main__":
manager = Manager()
graf_control = manager.dict()
graf_control['1'] = 0
graf_control['2'] = 0
graf_control['3'] = 0
print(graf_control)
p1 = Process(target=main, args=(str(1), graf_control,))
p2 = Process(target=main, args=(str(2),graf_control,))
p3 = Process(target=main, args=(str(3),graf_control,))
p1.start()
sleep(1)
p2.start()
sleep(1)
p3.start()
p1.join()
p2.join()
p3.join()
But I got an error:
AttributeError: 'NoneType' object has no attribute '_registry'
I didn't find a solution to this error and I need help to get the code running. Are there any ways to do this?

As per #Darkonaut comment, use graf_dict.keys() like so:
...
for key in graf_dict.keys():
...

python update variable in loop and use it in another process

Why while loop is ignored in work1? I would like to update value from string to another value in loop and output this value in process work2. Also already tried with Queue, but problem is I have only one variable which I would like to update in work1 and access to it at work2.
from multiprocessing import Process, Manager, Value
from ctypes import c_char_p
import time
def work1(string):
i = 2
string.value = i
# while True:
# print("work1")
# string.value = i + 1
# time.sleep(2)
def work2(string):
while True:
print("Value set in work1 " + str(string.value))
time.sleep(2)
if __name__ == '__main__':
manager = Manager()
string = manager.Value(int, 0);
p1=Process(target=work1, args=(string,))
p1.start()
p1.join()
p2=Process(target=work2, args=(string,))
p2.start()
p2.join()

That is because you didn't make your program parallel with two processes, but instead, two processes run in tandem. What you need to do is to start both process before any join. Like my modification below:
from multiprocessing import Process, Manager, Value
from ctypes import c_char_p
import time
def work1(string):
i = 2
string.value = i
while True:
i = i+1
string.value = i
print("work1 set value to "+str(string.value))
time.sleep(2)
def work2(string):
while True:
print("Value set in work1 " + str(string.value))
time.sleep(2)
if __name__ == '__main__':
manager = Manager()
string = manager.Value(int, 0, lock=False);
p1=Process(target=work1, args=(string,))
p2=Process(target=work2, args=(string,))
p1.start()
p2.start()
p2.join()
p1.join()
Indeed, if you write the code in this way, the join never happened due to the infinite while loop.

Python; unable to run multiple processes

I'm trying to run 2 separate processes in my python application. So I have code like this:
from multiprocessing import Process
def f1():
while 1:
print('Hello')
def f2():
while 1:
print('Goodbye')
def main():
p1 = Process(target=f1, args=())
p1.start()
p1.join()
p2 = Process(target=f2, args=())
p2.start()
p2.join()
if __name__ == '__main__':
main()
This code does nothing on my machine, it doesn't produce any output. I thought initially that maybe it was an IDE-related problem, but it's the same on both my IDEs, PyScripter and IDLE.
Any ideas, why this doesn't print anything?

How about using Queue?
from multiprocessing import Process, Queue
def f1(q):
while 1:
q.put('Hello')
def f2(q):
while 1:
q.put('Goodbye')
def main():
q = Queue()
p1 = Process(target=f1, args=(q,))
p1.start()
p2 = Process(target=f2, args=(q,))
p2.start()
while True:
try:
print q.get()
except:
break
if __name__ == '__main__':
main()

You should save it and run outside the IDE:
C:\> python multi.py
then it infinitely prints out Hello. You should change your main to see both Hello and Goodbye:
def main():
p1 = Process(target=f1, args=())
p2 = Process(target=f2, args=())
p1.start()
p2.start()
p1.join()
p2.join()
Then you have a little happy race condition that constantly prints out GHoodbyeello because both processes use the same stdout resource concurrently.