At 01:19 PM 8/15/2006 +1200, Greg Ewing wrote:
>Phillip J. Eby wrote:
>
> > The examples there are very short
>>and simple; in fact the complete Message implementation, including
>>imports and overload declarations is only *6 lines long*.
>>So, my only guess is that the people who looked at that skimmed right
>>past it, looking for something more complicated!
>
>If it really is that short and simple, why not just post
>the whole thing? Then there's no danger of anyone getting
>lost in parts of the documentation they're not supposed
>to be looking at.
Here are the most relevant bits excerpted from the text:
To create a new kind of metadata, we need to create a class that represents
the metadata, and then add a method to the ``binding.declareAttribute()``
generic function. For our example, we'll create a ``Message`` metadata type
that just prints a message when the metadata is registered::
>>> class Message(str):
... pass
>>> def print_message(classobj, attrname, metadata):
... print metadata, "(%s.%s)" % (classobj.__name__, attrname)
>>> binding.declareAttribute.addMethod(Message,print_message)
Now, we'll see if it works::
>>> class Foo: pass
>>> binding.declareAttribute(Foo, 'bar', Message("testing"))
testing (Foo.bar)
In addition to defining your own metadata types, ``declareAttribute()`` has
built-in semantics for ``None`` and sequence types. The former is a no-op, and
the latter re-invokes ``declareAttribute()`` on the sequence contents::
>>> binding.declareAttribute(Foo, 'baz',
... [Message('test1'), Message('test2')]
... )
test1 (Foo.baz)
test2 (Foo.baz)
>>> binding.declareAttribute(Foo, 'spam', None) # no-op
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