Hi, On Thu, Dec 17, 2009 at 10:15 AM, Martijn Faassen <faassen@startifact.com> wrote:
* It'd be nice if __call__ came back with a LookupError instead of a TypeError, but how to get from A to B without breakage?
Maybe I've misunderstanding, but what's the advantage of making IFoo(x) raise a LookupError instead of a TypeError? I've tried to follow the thread but I've been confused about this. I do rely on catching TypeErrors quite often in my code -- I had thought it was intended as part of the API. I like that treating it as typecasting instead of lookup blurs the conceptual distinction between "adapting x to IFoo" and "asserting x implements IFoo directly" -- when I actually want to know one or the other I can use explicit adaptation or check providedBy. In other words I use IFoo(x) when I don't care whether IFoo(x) == x. I suppose it's not a big deal but catching LookupErrors instead would feel somewhat less semantic for the way I think about this. But from what I've caught of the larger thread it sounds like I'm in the minority here. -Ethan