When does my function will go to previous scopes to look for a variable?

Question

in python 3.0 from what i know when i’m using variables that aren’t found in the local scope it will go all the way back until it reaches the global scope to look for that variable.

I have this function:

def make_withdraw(balance):
    def withdraw(amount):
        if amount>balance:
            return 'insuffiscient funds'
        balance=balance-amount
        return balance
    return withdraw

p=make_withdraw(100)
print(p(30))

When i insert a line:

nonlocal balance

under the withdraw function definition it works well,
but when i don’t it will give me an error that i reference local variable ‘balance’ before assignment, even if i have it in the make_withdraw function scope or in the global scope.

Why in other cases it will find a variable in previous scopes and in this one it won’t?

Thanks!

Asked By: argamanza

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Answer 1

There are too many questions on this topic. You should search before you ask.

Basically, since you have balance=balance-amount in function withdraw, Python thinks balance is defined inside this function, but when code runs to if amount>balance: line, it haven’t seen balance‘s definition/assignment, so it complains local variable 'balance' before assignment.

nonlocal lets you assign values to a variable in an outer (but non-global) scope, it tells python balance is not defined in function withdraw but outside it.

Answered By: laike9m

When does my function will go to previous scopes to look for a variable?

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