Problem with global variable not being assigned before I reference it

Question

I have this code regarding the fibonacci sequence and wriing an n number of fibonacci numbers to a file. I was wondering why I am getting an unbound local error here. It says I am referencing the variable fib_called before assignment.

fib_called = False
def global_fib(n, filename):
    global gf
    gf = load_fib(filename)
    i = 0
    write_fib(filename)
    while i < n:
        fib()
        write_fib(filename)
        i += 1
    return return_fib()

import os
def fib():
    if len(gf) == 1:
        gf.append(1)
else:
    gf.append(int(gf[-1] + gf[-2]))
fib_called = not fib_called    


def write_fib(filename):
    if fib_called == True:
        filename.open('w')
        filename.write(str(gf[-1]) + ' ')
    fib_called = not fib_called


def load_fib(filename):
    if os.path.exists(filename):
        filename.open('r')
        content == filename.read()
        return list(content) 
    else:
        f = open("newfile",'w')
        f.write('0' + ' ')
        return [0]   

def return_fib():
    return gf[-1]

looks like you have some indention problems in the fib() function? — crimson589
– crimson589, Commented Nov 26, 2020 at 3:23
You're not saying that fib_called should be global in function write_fib. That makes it a local variable with the same name. A local variable in which you read from before you assign it. Hence the error — Ted Klein Bergman
– Ted Klein Bergman, Commented Nov 26, 2020 at 3:30
In write_fib function, you need to declare fib_called as global. global variables could be referenced in local function but need to declare using global when trying to assign the value — Yuri R
– Yuri R, Commented Nov 26, 2020 at 3:33

Yuri R · Accepted Answer · 2020-11-26 03:39:58Z

You need to add global fib_called to fib and write_fib functions.

fib_called = False
def global_fib(n, filename):
    global gf
    gf = load_fib(filename)
    i = 0
    write_fib(filename)
    while i < n:
        fib()
        write_fib(filename)
        i += 1
    return return_fib()

import os
def fib():
    global fib_called

    if len(gf) == 1:
        gf.append(1)
    else:
        gf.append(int(gf[-1] + gf[-2]))

    fib_called = not fib_called    


def write_fib(filename):
    global fib_called

    if fib_called == True:
        filename.open('w')
        filename.write(str(gf[-1]) + ' ')
    fib_called = not fib_called


def load_fib(filename):
    if os.path.exists(filename):
        filename.open('r')
        content == filename.read()
        return list(content) 
    else:
        f = open("newfile",'w')
        f.write('0' + ' ')
        return [0]   

def return_fib():
    return gf[-1]

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