What is the Python equivalent of static variables inside a function?

Question

What is the idiomatic Python equivalent of this C/C++ code?

void foo()
{
    static int counter = 0;
    counter++;
          


        

Answer 1

Using an attribute of a function as static variable has some potential drawbacks:

• Every time you want to access the variable, you have to write out the full name of the function.
• Outside code can access the variable easily and mess with the value.

Idiomatic python for the second issue would probably be naming the variable with a leading underscore to signal that it is not meant to be accessed, while keeping it accessible after the fact.

An alternative would be a pattern using lexical closures, which are supported with the nonlocal keyword in python 3.

def make_counter():
    i = 0
    def counter():
        nonlocal i
        i = i + 1
        return i
    return counter
counter = make_counter()

Sadly I know no way to encapsulate this solution into a decorator.