Weird scoping error

[Stef]

I bumped into this weird scoping error and I have no clue what's going on.

#module main

FIXED = 0               # banks spend a fixed amount into the economy
PROFIT_PERCENTAGE = 1   # banks spend a percentage of their profit into the economy
CAPITAL_PERCENTAGE = 2  # banks spend a percentage of their capital into the economy

SPENDING_MODES = [FIXED, PROFIT_PERCENTAGE, CAPITAL_PERCENTAGE]

fixed = 5.00    # fixed amount that banks spend into the real economy, adjusted for inflation
pp = 0.20       # percentage of profit that banks spend into the real economy
cp = 0.20       # percentage of capital that banks spend into the real economy

mr = 0.04 # minimum reserve

pbdr = 0.01 # private bank payback rate
nbdr = 0.05 # non bank payback rate

ecbi = 0.01 # ECB interest rate
pbi = 0.02  # private bank interest rate

g = 0.00  # growth rate of available money. This is money that circulates in the real economy
f = 0.02  # inflation

im1 = [] # inside money on bank's account
im2 = [] # inside money that is on non bank accounts

debt = [] # outstanding debt on which interest is paid

om1 = [] # outside money on ECB account
om2 = [] # outside money on private banks' account

bank_profit = []    # bank profit: income from interest - payoff of loans and interests to ECB
bank_spending = []  # money banks spend into the real economy
bank_debt = []      # outstanding debt of banks to the ECB

growth = [] # growth per cycle
om_growth = [] # om growth per cycle


def runSimulation(initial_m2):
    for spending_mode in SPENDING_MODES:
        for i in range(500):
            if i == 0:
                initialize(initial_m2)
            else:
                # copy previous state
                im1.append(im1[i - 1])
                im2.append(im2[i - 1])
                debt.append(debt[i - 1])

                om1.append(om1[i - 1])
                om2.append(om2[i - 1])
                bank_profit.append(0.0)
                bank_spending.append(0.0)
                bank_debt.append(bank_debt[i - 1])
# rest of code of this function is omitted

def initialize(initial_im2):
    im1.clear()
    im2.clear()
    debt.clear()

    om1.clear()
    om2.clear()
    bank_profit.clear()
    bank_spending.clear()
    bank_debt.clear()

    growth.clear()
    om_growth.clear()

    im1.append(0.0)
    im2.append(initial_im2)
    debt.append(initial_im2)

    om1.append(0.0)
    reserve = round(initial_im2 * mr, 2)
    om2.append(reserve)
    bank_profit.append(0.0)
    bank_spending.append(0.0)
    bank_debt.append(reserve)

    growth.append(0.0)
    om_growth.append(0.0)

It concerns the bank_spending variable when I first use it in the runSimulation() method. I get the following error on it:
bank_spending.append(0.0)
UnboundLocalError: local variable 'bank_spending' referenced before assignment

I have no clue why! The variabel is defined in the global scope, just like for example bank_profit is. Why do I get this error while all the other variables don't pose a problem?

Hope someone can clear this mystery for me. I'm fairly new to Python but have an extensive programming background and I know how scoping works. Must be something stupid I just don't see.

Thanks in advance,
Stef

[ichabod801]

I'm not getting any scoping problems running that code. I think the obvious solution would be not to depend on global scope. Put all the data in a dictionary and pass it explicitly as a parameter, or wrap the whole simulation code in a class.

[perfringo]

You can read about it for example in this StackOverflow thread

Long story short: give names you want modify as parameters/arguments to function

---

EDIT: How it is explained in Python documentation

[Stef]

Thanks for the answers. It led to actually figuring out what was going on. Somewhere in the code that I had omitted from the post I accidentally made an assignment to bank_spending instead of to bank_spending[i], as was the intention.

Thanks people!
Stef