Globals in nested functions

[Duncan Booth]

"jm.suresh at no.spam.gmail.com" <jm.suresh at gmail.com> wrote:

> def f():
>     a = 12
>     def g():
>         global a
>         if a < 14:
>             a=13
>     g()
>     return a
> 
> print f()
> 
> This function raises an error. Is there any way to access the a in f()
> from inside g().
> 
> I could find few past discussions on this subject, I could not find
> the simple answer whether it is possible to do this reference.
> 
'global' means global to the module, it prevents the lookup happening in 
current or nested scopes.

Simple answer:

You can access an object referenced by a nested scope variable and you 
can mutate the object accessed in that way, but you cannot rebind the 
name to a different object without resorting to hackery.

To get the effect you want, simply use a mutable object:

>>> def f():
    class v:
        a = 12
    def g():
        if v.a < 14:
            v.a=13
    g()
    return v.a

>>> f()
13

and as soon as the code starts looking at all complex, refactor that so 
the class is the thing you interact with:

>>> class F(object):
    def g(self):
        if self.a < 14:
            self.a = 13
    def __call__(self):
        self.a = 12
        self.g()
        return self.a

>>> f = F()
>>> f()
13