> Fredrik Lundh <fredrik at pythonware.com> wrote:
>
> > George Sakkis wrote:
> >
> > > 1) why having a "generic operation" len() that ends up looking for an
> > > ugly special *method* called __len__() makes sense, while calling
> > > directly a method len() doesn't
> >
> > for the very reason Mike explained: keeping implementation interfaces
> > separate from public interfaces has allowed Python to avoid a certain
> > category of design fragmentation that other languages suffer from.
>
> Fredrik, I am not arguing for the argument's sake, I just don't get
> it: Python requires my class to define __len__, otherwise len() fails.
> Why not require len() as a method instead and forget about __len__ ?
> Does len() (the function) do anything smarter behind the scenes than
> just passing the ball to __len__ ? That could justify its role but
> AFAIK it doesn't.
>
> George
So you're suggesting something like:
class Lengthable:
def len(self):
raise NotImplemented
(presumably defined in some "standard" or "builtins" module) be a
mix-in to every type which it currently makes sense to call "len()"
on?
Bill
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