On Thu, 2 Nov 2017 10:13 am, Jason Maldonis wrote:
> Hi everyone,
>
> I want to use a metaclass to override how class instantiation works. I've
> done something analogous to using the Singleton metaclass from the Python3
> Cookbook example.
In my opinion, nine times out of ten, using a metaclass for something like
that is overkill.
(And that's putting aside the fact that 999 out of a thousand, using a
Singleton is the wrong solution, no matter what the question is.)
> However, I want to provide a classmethod that allows for "normal" class
> instantiation that prevents this metaclass from being used.
To me, that strongly suggests that a metaclass is the wrong solution.
> To do that, I think I just make a @classmethod constructor function.
> However, I can imagine a few different ways of writing this:
>
> @classmethod
> def normal_constructor(cls, *args, **kwargs):
> return type.__call__(*args, **kwargs)
Untested, but I think that should be:
return type.__call__(cls, *args, **kwargs)
> @classmethod
> def normal_constructor(cls, *args, **kwargs):
> return super(???).__call__(*args, **kwargs) # I'm not sure what should
> go in the super here (I'm using python3)
>
> @classmethod
> def normal_constructor(cls, *args, **kwargs):
> self = cls.__new__(cls)
> self.__init__(*args, **kwargs)
> return self
>
> Is one of these correct? Or do they all do the same thing?
None of them look "correct", they all look "weird and scary" :-)
If I had to pick one of these three -- and I hope that I would not -- I'd pick
the first one.
> I was looking for documentation for what exactly `type.__call__` does so
> that I can emulate it,
And then if type.__call__ changes, your emulation will be wrong.
> but I wasn't able to find any docs explicitly
> detailing what that method does. If someone knows where this info is that
> would be great too.
--
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.
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