"Steven Bethard" <[EMAIL PROTECTED]> wrote:
> On 12/9/06, Josiah Carlson <[EMAIL PROTECTED]> wrote:
> > I'd prefer to see...
> >
> > class MyMapping:
> > @implements(mapping)
> > def __getitem__(self, key):
> > ...
> >
> > @implements(mapping)
> > def __len__(self):
> > ...
> >
> [snip]
> >
> > P.S. Here's a 10 minute implementation of the above semantics that is
> > *almost* backwards compatible with Python 2.3 (except for the decorator
> > thing, which Python 2.3 has to do without).
[snip]
> > __builtins__.type = type
>
>
> Sorry, I don't understand this implementation. I just tried it and
> the following fails because ``__getitem__`` is now an
> ``implements_wrapper`` that accepts the wrong arguments::
>
> class C(object):
> @implements(mapping)
> def __getitem__(self, item):
> return 42
>
> C()[1]
It doesn't work because we need to replace the base metaclass from
object, which the above mechanism doesn't do. It half-asses it by
monkey-patching __builtins__, but object.__new__ doesn't look in
__builtins__, it uses CPython calls.
If you want to get your above use to work all the time (I believe, I
hadn't tested it), you can also add the following just after the
__builtins__.type = type .
class object(object):
__metaclass__ = type
__builtins__.object = object
> But I think the ``implements()`` decorator is a good way to approach
> this. Here's a different approach to it::
[snip]
> class C(object):
> __metaclass__ = interface_monitor
>
> @implements(Mapping)
> def __getitem__(self, key):
> return 4
>
> @implements(Mapping)
> def __iter__(self):
> return [4, 4, 4]
>
> Note that with this code, an interface is just a set of methods, so
> you can use ``supports()`` equally well to check for support of
> individual methods or to check support for whole sets of methods.
That's what I was getting at with the previous version, though instead
of using methods on the various interface objects (eg Mapping), I used
objects in the class namespace. Using a function does allow for doing
argument list length and/or keyword name verification, but I don't know
if we want to go that far.
Using the monkey patching of __builtins__.object as I include in this
message, makes the __metaclass__ bit that you use unnecessary.
I also have a personal aversion for adding *yet another* attribute to
the methods that implement interfaces, but since we are adding
__signature__, etc., and no one else seems to be complaining, what's one
more?
- Josiah
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