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On Fri, May 19, 2017 at 11:24:53AM -0700, Guido van Rossum wrote:
Easily allow to specify a conversion function. For example I have some code like below: note that I can store a numpy array while keeping hashability and I can make it convert to a numpy array in the constructor.
@attr.s(cmp=False, hash=False) class SvgTransform(SvgPicture): child = attr.ib() matrix = attr.ib(convert=numpy.asarray)
I find that completely enigmatic, there's far too much implicit behaviour going on behind the scenes. I couldn't even begin to guess what SvgTransform as a class does, or what SvgTransform.child and SvgTransform.matrix are.
I suppose that's okay for experts to whom the attrs module is second nature, but I think this approach is far too "magical" for my tastes. Instead of trying to cover every possible use-case from a single decorator with a multitude of keyword arguments, I think covering the simple cases is enough. Explicitly overriding methods is not a bad thing! It is much more comprehensible to see an explicit class with methods than a decorator with multiple keyword arguments and callbacks.
I like the namedtuple approach: I think it hits the sweet spot between "having to do everything by hand" and "everything is magical".