Chris Angelico <ros...@gmail.com> writes:
> On Sat, 24 Sept 2022 at 07:52, Meredith Montgomery
> <mmontgom...@levado.to> wrote:
>>
>> def Counter(name = None):
>> o = {"name": name if name else "untitled", "n": 0}
>> def inc(o):
>> o["n"] += 1
>> return o
>> o["inc"] = inc
>> def get(o):
>> return o["n"]
>> o["get"] = get
>> return o
>>
>
> Want a neat demo of how classes and closures are practically the same thing?
>
> def Counter(name=None):
> if not name: name = "untitled"
> n = 0
> def inc():
> nonlocal n; n += 1
> def get():
> return n
> return locals()
>
> Aside from using a nonlocal declaration rather than "self.n", this is
> extremely similar to classes, yet there are no classes involved.
>
> A class statement creates a namespace. The locals() function returns
> the function's namespace.
>
> Each call to Counter() creates a new closure context, just like each
> call to a constructor creates a new object.
>
> There's very little difference, at a fundamental level :)
I started out this way, but I had to change direction to implement
inheritance: the difficulty with closures seems to be lexical scoping,
which makes it hard (or impossible) for me to move these closures to
another ``object''. For instance, the nonlocal /n/ in /inc/ above is
forever bound to that closure; there seems to be no way to make /inc/
update some /n/ in another ``object'', which is needed in my conception
of inheritance. I think Python would have to let me duplicate closures.
(Thanks for showing me /locals()/.)
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