changing global variable with thread in Python

Question

I am trying to write a script updating a global variable every 10 seconds. For simplicity let's just increment q once teach time

import time, threading

q = 0
def f(q):
    # get asset position every 10 seconds:
    q += 1
    print q

    # call f() again in 10 seconds
    threading.Timer(10, f).start()


# start calling f now and every 10 sec thereafter
f(q)

Instead python says:

UnboundLocalError: local variable 'q' referenced before assignment

What is the correct way to change the variable q?

this example uses threading, doesn't update any values. Run certain code every n seconds

Put `global q` at the top of the `f` function. – dano Jul 23 '14 at 01:30 — dano, Jul 23 '14 at 01:30
@dano I didn't know you could do that in Python. Thanks – john mangual Jul 23 '14 at 01:34 — john mangual, Jul 23 '14 at 01:34

score 4 · Accepted Answer · answered Jul 23 '14 at 01:38

4

You need to explicitly declare q as a global. q += 1 confuses the interpreter otherwise.

import threading

q = 0
def f():
    global q
    q += 1
    print q
    threading.Timer(10, f).start()

f()

answered Jul 23 '14 at 01:38

Andrew Johnson

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changing global variable with thread in Python

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