python - update thread variable

Question

how do I update a variable inside a running thread, which is an infinite loop based on such variable?
a simplified version of what I tried is what follows, to no results of course, and I can't find any pointer.

import some_module as mod
import threading

class thr (threading.Thread):
    NUM = 5  # set a default value to start the script
    def run (self):
        mod.NUM = NUM
        mod.main_loop()

try:
    thr().start()
    time.sleep(1)
    thr().NUM = 2
    time.sleep(1)
    thr().NUM = 6
    time.sleep(1)
    thr().NUM = 8

6502 · Accepted Answer · 2016-06-01 20:43:20Z

1

The problem is that you're creating a new thread each time you "call" (i.e. instantiate) thr. Change your code to

t = thr()
t.start()
time.sleep(1)
t.NUM = 2
time.sleep(1)
t.NUM = 6
time.sleep(1)
t.NUM = 8
time.sleep(1)

answered Jun 1, 2016 at 20:43

6502

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7 Comments

nxet Over a year ago

unfortunately it still doesn't update the variable inside the infinite loop

6502 Over a year ago

It updates the NUM variable in the thread object instance... to update mod.NUM just do that with mod.NUM = 2 ... etc.

nxet Over a year ago

that far I've gotten already, my problem here is that the updated variable is not being fed to the infinite loop...

6502 Over a year ago

@nxet: what loop? you're asking what is the problem in code not shown? My wild guess is that the statement at line 42 in some_module.py contains a mistake... but it's a VERY wild guess :-D

nxet Over a year ago

man I was this close to open up some_module.py and see for any error there :/ this is how lost I am here. basically the thread I'm launching has an infinite loop within, and the variable I want to update is what the loop parses to execute. I thought it was irrelevant, but at this point it might be worth noting that some_module.py actually is a multiplexing script. basically I say '5 7' to the module, and it runs infinitely multiplexing said values between two led bars (extremely roughly explained). I need to update the value and see the change reflected with the leds

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MartinP · Accepted Answer · 2016-06-02 08:15:11Z

0

Maybe try use queue for change NUM variable.

https://docs.python.org/2/library/queue.html

Check examples here :

https://pymotw.com/2/Queue/

Generally speakinig the queue allows You send data between threads. Use get() for getting data from queue and put() for put data to queue.

edited Jun 2, 2016 at 8:15

answered Jun 1, 2016 at 21:57

MartinP

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3 Comments

nxet Over a year ago

I'm afraid that's a bit too generic for my limited knowledge of the language, and reading the link provided didn't help much unfortunately. can you please elaborate a bit more on this? thanks a lot

nxet Over a year ago

the second link was way more helpful. but am I wrong to assume I'm forced to kill and spawn a new thread everytime?

MartinP Over a year ago

@nxet I don`t uderstand :)What mean - "I'm forced to kill and spawn a new thread everytime?"

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