[PyQt] dip model types, properties, and syntax

[Darren Dale]

On Wed, Aug 25, 2010 at 1:17 PM, Phil Thompson
<phil at riverbankcomputing.com> wrote:
> On Sat, 14 Aug 2010 08:45:13 +0100, Phil Thompson
> <phil at riverbankcomputing.com> wrote:
>> On Mon, 9 Aug 2010 09:45:12 -0400, Darren Dale <dsdale24 at gmail.com>
> wrote:
>>> I have a question about using dip model attributes as properties. The
>>> documentation at
>>>
>>
> http://www.riverbankcomputing.com/static/Docs/dip/model_tutorial.html#attributes-are-properties
>>> gives an example:
>>>
>>> class ExampleModel(Model):
>>>
>>>     name = Str
>>>
>>>     def _get_name(self):
>>>         return self._name
>>>
>>>     def _set_name(self, value):
>>>         self._name = value
>>>
>>>     # method taken from previous section in documentation:
>>>     def _default_name(self):
>>>         import name_database
>>>         return name_database.most_common_name()
>>>
>>>
>>> Would it be possible for dip's model types to support the property
>>> decorator syntax introduced in Python-2.6? If so, the above example
>>> could then be implemented as:
>>>
>>> class ExampleModel(Model):
>>>
>>>     name = Str
>>>
>>>     @name.getter
>>>     def name(self):
>>>         return self._name
>>>
>>>     @name.setter
>>>     def name(self, value):
>>>         self._name = value
>>>
>>>     @name.default
>>>     def name(self):
>>>         import name_database
>>>         return name_database.most_common_name()
>>>
>>> The virtue, aside from reusing an already familiar pattern in the
>>> standard library, is that the ExampleModel namespace has fewer exposed
>>> private methods, which is desirable for models intended to be used and
>>> inspected in an interactive python environment like IPython.
>>
>> Hmm - interesting. It's more verbose but it is nicer. It could also
>> support observers and allow declarative observers across classes. It may
>> also be faster.
>
> Unfortunately I can't think of a way to implement it. The problem arises
> because "name = Str" is allowed as a shortcut for "name = Str()" and there
> doesn't seem to be a way to implement (for example) getter() so that it can
> cope with the different cases.

Hmm. What if BaseType or ValueType did something like:

    @classmethod
    def property(cls, val):
        if type(val) == types.FunctionType:
            return property_factory(cls, getter=val)
        else:
            res = property_factory(cls, default=val)
            return res.getter

That may let you do:

class Test(model):
    @Str.property
    def name(self):
        return self._name

or

class Test(model):
    #provide the default:
    @Str.property('foo')
    def name(self):
        return self._name

Is that a crazy idea?

Darren