Function to avoid a global variable

[Bob van der Poel]

I still think that the use of a keyword like "static" would be easiest.

def foo(arg):
    static counter = 0
    counter += 1
    if counter ...

And in this case static just means that it's a variable only readable
inside foo() and it should maintain it's value between calls. A "global"
without the name pollution. Or is this too simple .... ???


On Fri, May 1, 2020 at 4:30 PM Chris Angelico <rosuav at gmail.com> wrote:

> On Sat, May 2, 2020 at 9:14 AM DL Neil via Python-list
> <python-list at python.org> wrote:
> >
> > On 28/04/20 7:36 PM, Chris Angelico wrote:
> > >>> "Best"? Not sure about that. Functions are first-class objects in
> > >>> Python, so a function *is* a callable object. You don't have to
> create
> > >>> a custom class with a call method just to be able to attach
> attributes
> > >>> to your function.
> > >>>
> > >>> ChrisA
> > >>>
> > >>
> > >> Using a mutable object as a function default parameter value
> > >> and changing it inside the function looks like a "trick"
> > >> according to me.
> > >
> > > Sure. But you're contrasting this to a suggestion to literally just
> > > attach attributes to a function. Python lets you actually do that. You
> > > don't have to simulate the feature by creating a custom class and
> > > making it callable - you just straight-up add attributes to a
> > > function. Sure, what you suggested works, but there's no reason to.
> >
> >
> > Functions are objects too! I regularly point-out this powerful facility,
> > and its affordances, but...
> >
> >
> > Yes, it's perfectly reasonable and even sensible to attach an attribute;
> > BUT do many people expect to find such? If we were to collectively
> > survey our own application code, how many examples would we find - as a
> > percentage of such a corpus?
> >
> > Expectation: it would be v.v.low. Accordingly, whilst
> > perfectly-implemented Python, and thus not a "trick", at least it is
> > something that is easy for 'an ordinary person' to 'miss' (or
> > misunderstand).
> >
>
> One of the problems with the use of function attributes is that
> there's no way to say "this function". You have to use its name.
> Otherwise, it would be easy to write self-contained idioms such as
> static variables or omitted arg detection without the risk of
> polluting the namespace:
>
> def some_function(x, y, z=object()):
>     if z is me.__defaults__[0]:
>         z = x + y
>     ...
>
> def static(**kw):
>     def deco(f):
>         for name, initial in kw.items():
>             setattr(f, name, initial)
>         return f
>     return deco
>
> @static(called=0)
> def other_function():
>     me.called += 1
>     ...
>
> Obviously the name "me" can't be used, as it'd break a bunch of code,
> but conceptually this would be incredibly helpful. It'd also be a
> reliable idiom for recursion optimization - any "me()" is guaranteed
> to be recursion and may potentially give info to an optimizer.
>
> Perhaps, if Python had a way to identify the current function, it
> would feel less odd to attach attributes to it.
>
> ChrisA
> --
> https://mail.python.org/mailman/listinfo/python-list
>


-- 

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