Can't access global variable in python -

i'm using multi processing library in python in code below:

from multiprocessing import process import os time import sleep delay  test = "first"  def f():     global test     print('hello')     print("before: "+test)     test = "second"  if __name__ == '__main__':     p = process(target=f, args=())     p.start()     p.join()     delay(1)     print("after: "+test)  

it's supposed change value of test @ last value of test must second, value doesn't change , remains first. here output:

hello before: first after: first 

the behavior you're seeing because p new process, not new thread. when spawn new process, copies initial process's state , starts executing in parallel. when spawn thread, shares memory initial thread.

since processes have memory isolation, won't create race-condition errors caused reading , writing shared memory. however, data child process parent, you'll need use form of inter-process communication pipe, , because fork memory, more expensive spawn. in computer science, have make tradeoff.

for more information, see:

• https://en.wikipedia.org/wiki/process_(computing)
• https://en.wikipedia.org/wiki/thread_(computing)
• https://en.wikipedia.org/wiki/inter-process_communication

based on you're trying accomplish, consider using threads instead.