global variable error in Python

Question

I am learning Python on my own and I am baffled on what is wrong in the following code

glob_var = 0

def print_glob_var():

    s = 0

    while glob_var > 0:
        s = s+1
        glob_var = glob_var - 1
    return s
    #print (globvar)     

def main():

    global glob_var    
    glob_var = 4
    print_glob_var()

main()

I am getting error "UnboundLocalError: local variable 'glob_var' referenced before assignment" . However when I use only the print the code block works fine.

What I am doing wrong. I am using Python 3.5.2

you're missing the global keyword inside the function body — danidee
– danidee, Commented Nov 6, 2016 at 11:42

barak manos · Accepted Answer · 2016-11-06 11:41:37Z

1

In order to change the value of a global variable inside a function, you must declare it global inside the function. You seem to do so in function main, but not in function print_glob_var.

answered Nov 6, 2016 at 11:41

barak manos

30.2k10 gold badges67 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Alex Hall · Accepted Answer · 2016-11-06 11:45:25Z

1

Python analyses the body of print_glob_var, sees an assignment to glob_var (specifically glob_var = glob_var - 1) and no global statement, and decides based on that that glob_var is a local variable that it expects to see defined within the function. If you remove the assignment you will no longer get this error, although of course that creates new problems. Alternatively you could add global glob_var to the function. Including it in main is not enough, you need that statement everywhere the variable is used.

This is the kind of reason that using non-constant global variables in Python is a bad idea. Learn about classes.

answered Nov 6, 2016 at 11:45

Alex Hall

36.2k5 gold badges63 silver badges98 bronze badges

Comments

ubundows · Accepted Answer · 2016-11-06 13:32:27Z

1

glob_var = 4

def print_glob_var():
    global glob_var        # Set glob_var as global
    s = 0

    while glob_var > 0:
        s = s+1            # You can do s += 1 here
        glob_var = glob_var - 1
        print(glob_var)    # Your commented out print() was after the return statement
    return s               # so it would never be reached.

def main():
    print_glob_var()

main()

edited Nov 6, 2016 at 13:32

answered Nov 6, 2016 at 11:57

ubundows

4316 silver badges11 bronze badges

Collectives™ on Stack Overflow

global variable error in Python

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related