When should I use local or nonlocal variables in Python?

Can you explain when to use local or nonlocal variables in Python?

Sure! Local variables are defined within a function and can only be accessed there. Nonlocal variables, on the other hand, are used in nested functions to refer to variables in the nearest enclosing scope that is not global.

Can you give me an example of using nonlocal variables?

Absolutely! Here's a simple example:

def outer_function():
    x = 'local'
    
    def inner_function():
        nonlocal x
        x = 'nonlocal'
        print(x)
    
    inner_function()
    print(x)

outer_function()

In this case, x is modified in the inner function and retains its new value in the outer function.

What happens if I try to use a nonlocal variable that hasn't been defined?

If you try to use a nonlocal variable that hasn't been defined in the enclosing scope, Python will raise a SyntaxError. You need to ensure that the variable exists in the outer function before you can use it as nonlocal.

Are there any performance implications of using nonlocal variables?

Using nonlocal variables can have some performance implications, as accessing them requires looking up the variable in the enclosing scope. However, in most cases, the difference is negligible unless you're working in a performance-critical section of code.