Python - How to reference a global variable from a function [duplicate]

问题

This question already has answers here:

How can I access global variable inside class in Python (5 answers)

Closed 6 years ago.

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!

回答1:

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()

来源：https://stackoverflow.com/questions/17928791/python-how-to-reference-a-global-variable-from-a-function