Pass boolean argument by reference

In C++ you can always pass something as reference and anything that happens within the callee would be known to caller by just examining the referenced variable.

Imagine this scenario:

def x():
   a = f()
   print(a)

def f():
   return "hello"

What I want is add a boolean flag that returns from f to x. There are several ways to do that:

1. make f return a tuple (str,bool)
2. pass a reference to a boolean variable into f

option 1 is currently not possible since there are many callers to f() and I cant change them to accept tuple as return value, so it must stay as it is.

option 2 is not possible since boolean argument is immutable (as I’ve learned recently).

Only f can calculate the boolean value, and x needs to know about it.

Is there any good way to achieve that? Looking for something that is not bad practice in Python coding in general.

>Solution :

The option that’s closest to passing a pointer/reference into f would be to pass it a mutable object, like a list:

def f(ok=None):
    if isinstance(ok, list):
        ok.append(True)
    return "hello"

def x():
    ok = []
    a = f(ok)
    print(a, ok.pop())

But the better solution IMO would be to return a tuple, and refactor that behavior into a new function so that you’re sharing code without disturbing the existing API:

def f_with_flag():
    return "hello", True

def f():
    return f_with_flag()[0]

def x():
    a, ok = f_with_flag()
    print(a, ok)