Why do I get a "referenced before assignment" error when assigning to a global variable in a function?

Question

In Python, I'm getting the following error:

UnboundLocalError: local variable 'total' referenced before assignment

At the start of the file (before the function where the error comes from), I declare total using the global keyword. Then, in the body of the program, before the function that uses total is called, I assign it to 0. I've tried setting it to 0 in various places (including the top of the file, just after it is declared), but I can't get it to work.

Does anyone see what I'm doing wrong?

Answer 1

I think you are using 'global' incorrectly. See Python reference. You should declare variable without global and then inside the function when you want to access global variable you declare it global yourvar.

#!/usr/bin/python

total

def checkTotal():
    global total
    total = 0

See this example:

#!/usr/bin/env python

total = 0

def doA():
    # not accessing global total
    total = 10

def doB():
    global total
    total = total + 1

def checkTotal():
    # global total - not required as global is required
    # only for assignment - thanks for comment Greg
    print total

def main():
    doA()
    doB()
    checkTotal()

if __name__ == '__main__':
    main()

Because doA() does not modify the global total the output is 1 not 11.