[Python-3000] Metaclasses in Py3K (original) (raw)

Josiah Carlson jcarlson at uci.edu
Mon Dec 18 01:44:42 CET 2006

(wasn't quite done with that last message, so I'll just update the parts where I wasn't finished)

Josiah Carlson <jcarlson at uci.edu> wrote:

Talin <talin at acm.org> wrote: > I don't see why any existing metaclasses would need to be re-written - > see below.

For people using the old syntax, yes, but the old syntax is going away (otherwise why offer new syntax?), so rewrites are necessary.

[snip slots stuff]

The above still has the ugliness of needing to state the name of the slots attributes as many times as in the original version, which was one of the complaints about slots use. That is to say, the same issue that existed with function decorators, exists today with slots. There are mechanisms to get around it (using one of the autoslots and attribute initializers in the Python cookbook)...

class X(object): metaclass = AutoSlots def init(self, x, y, z): InitAttrs(self, locals()) However, I've not been convinced that

I've not been convinced that removing metaclass and slots is necessarily a good idea. Yes, they are ugly. But they work. And they offer a big HEY SOMETHING IS SPECIAL HERE marker.

If the point of the syntax change is to remove ugly, fine. But I think that the point of changing what exists is to make life easier for people. Easier to write, maintain, and understand.

Removing for the sake of removing ugly, your "x = y = z = Slots" works fine, but it doesn't make understanding it any easier. It seems like magic, and the semantics smells quite a bit like the "assignment decorators" proposal. But maybe that's just me.

Is slots and metaclass magic? Sure, but only as much as all other meth definitions (which aren't going away in Py3k). The real trick is that the magic is warned about via the use of double leading and trailing underscores. Removing the magic warning isn't helpful, especially if it is only to remove ugly.

[snip done parts]

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