Python - How to reference a global variable from a function

Question

I must be missing some very basic concept about Python's variable's scopes, but I couldn't figure out what.

I'm writing a simple script in which I would like to access a variable that is declared outside the scope of the function :

counter = 0

def howManyTimesAmICalled():
    counter += 1
    print(counter)

howManyTimesAmICalled()

Unexpectedly for me, when running I get :

UnboundLocalError: local variable 'counter' referenced before assignment

Adding a global declaration at the first line

global counter
def howManyTimesAmICalled():
    counter += 1
    print(counter)

howManyTimesAmICalled()

did not change the error message.

What am I doing wrong? What is the right way to do it?

Thanks!

Did you add `global counter` in the first line of the `howManyTimeAmICalled` function ? — karthikr, Jul 29 '13 at 16:07
@karthikr - I have edited my question to make it clear. Sukrit Kalra 's answer clarifies that indeed it is in the wrong place. — Ohad Dan, Jul 29 '13 at 16:10

score 8 · Accepted Answer · answered Jul 29 '13 at 16:06

8

You need to add global counter inside the function definition. (Not in the first line of your code)

Your code should be

counter = 0

def howManyTimesAmICalled():
    global counter
    counter += 1
    print(counter)

howManyTimesAmICalled()

answered Jul 29 '13 at 16:06

Sukrit Kalra

2

fyi: that signals to use the counter from the global registry rather than the local one – Eiyrioü von Kauyf Jul 29 '13 at 16:10

1 Answers1