如何在使用多处理时动态更改函数中变量的值

Question

how can i dynamically change the value of lis so that every second it'll output a list in which the last element is 2x the last element of the previous list.

import time, multiprocessing

lis = [1, 2, 4]

def printer():
    while True:
        print(lis)
        time.sleep(1)

def updater():
    while True:
        time.sleep(1)
        lis.append(lis[-1]*2)

if __name__ == '__main__':
    process1 = multiprocessing.Process(target=updater)
    process2 = multiprocessing.Process(target=printer)

    process1.start()
    process2.start()

    process1.join()
    process2.join()

i need the output to be something like this

[1, 2, 4]
[1, 2, 4, 8]
[1, 2, 4. 8. 16]
[1, 2, 4, 8, 16, 32] 
.
.

but right now the output is

[1, 2, 4]
[1, 2, 4]
[1, 2, 4]
[1, 2, 4] 
.
.

I tried using global lis but that didnt work either.

Answer 1

You can achieve desired behavior using multiprocessing.Manager .

Managers provide a way to create data which can be shared between different processes. You can read more about it here .

Based on example from Server process section you can rewrite your code like this:

import time, multiprocessing


def printer(_lis):
    while True:
        print(_lis)
        time.sleep(1)

def updater(_lis):
    while True:
        time.sleep(1)
        _lis.append(_lis[-1]*2)

if __name__ == '__main__':
    with multiprocessing.Manager() as manager:
        lis = manager.list([1, 2, 4])
        process1 = multiprocessing.Process(target=updater, args=(lis,))
        process2 = multiprocessing.Process(target=printer, args=(lis,))

        process1.start()
        process2.start()

        process1.join()
        process2.join()