On 06Jan2016 18:57, ALAN GAULD <alan.ga...@btinternet.com> wrote:
On 06/01/16 14:46, Steven D'Aprano wrote:
It would be reasonable to make this a factory function declared in the
global module level. But I think making it a classmethod is better.
I won't put up much of an argument here. In C++ or Java I'd
definitely say use a class method. But it seems to me that I've
seen more factory functions in modules than class method factories.
But that's not been a detailed analysis just a gut feel for what
seems idiomatic in Python. It also seems easier for beginners
to grasp than the more esoteric notion of class methods.
Most of my factories are global functions, but that is mere historic artifact.
As a direct consequence of explaining this to Alex Kleider I'm moving
aggressively to using @classmethod for this, naming them ".from_*" unless I
have some amazing reason not to.
... ensures that if you subclass the class, you automatically
get a valid constructor as well.
Wouldn't it return an instance of the superclass rather than
the sub class? You'd need to override it wouldn't you?
No, when you call:
SubClass.from_blah(...)
where from_blah is defined in the superclass, the leading "cls" parameter is
the subclass because you invoked it through the subclass, just as you get the
leading "self" instance parameter when you invoke an instance method through
the instance. That's one reason that @classmethod is so nice here.
Cheers,
Cameron Simpson <c...@zip.com.au>
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