How to share data between Python processes?

This is one simple example from python documentation -

from multiprocessing import Process, Queue

def f(q):
    q.put([42, None, 'hello'])

if __name__ == '__main__':
    q = Queue()
    p = Process(target=f, args=(q,))
    p.start()
    print q.get()    # prints "[42, None, 'hello']"
    p.join()

You can use pipe as well, Refer for more details - https://docs.python.org/2/library/multiprocessing.html

Fom 3.8 it is possible to use shared_memory. This example is taken from the docs:

>>> from multiprocessing import shared_memory
>>> shm_a = shared_memory.SharedMemory(create=True, size=10)
>>> type(shm_a.buf)
<class 'memoryview'>
>>> buffer = shm_a.buf
>>> len(buffer)
10
>>> buffer[:4] = bytearray([22, 33, 44, 55])  # Modify multiple at once
>>> buffer[4] = 100                           # Modify single byte at a time
>>> # Attach to an existing shared memory block
>>> shm_b = shared_memory.SharedMemory(shm_a.name)
>>> import array
>>> array.array('b', shm_b.buf[:5])  # Copy the data into a new array.array
array('b', [22, 33, 44, 55, 100])
>>> shm_b.buf[:5] = b'howdy'  # Modify via shm_b using bytes
>>> bytes(shm_a.buf[:5])      # Access via shm_a
b'howdy'
>>> shm_b.close()   # Close each SharedMemory instance
>>> shm_a.close()
>>> shm_a.unlink()  # Call unlink only once to release the shared memory

However you should be carefull with the race conditions, I personally recommend a message system or join as mentioned in other answers. However, if you only have one writting process and the rest are readers, it should be quite safe.

Here's an example of multiprocess-multithread and sharing a couple variables:

from multiprocessing import Process, Queue, Value, Manager
from ctypes import c_bool
from threading import Thread


ps = []

def yourFunc(pause, budget):
    while True:
        print(budget.value, pause.value)
        ##set value
        pause.value = True  
        ....

def multiProcess(threads, pause, budget):
    for _ in range(threads):
        t = Thread(target=yourFunc(), args=(pause, budget,)) 
        t.start()
        ts.append(t)
        time.sleep(3)

if __name__ == '__main__':
    pause = Value(c_bool, False)
    budget = Value('i', 5000)

    for i in range(2):
        p = Process(target=multiProcess, args=(2, pause, budget))
        p.start()
        ps.append(p)