[Python-ideas] of properties and metaclasses
taleinat at gmail.com
Tue Jul 24 12:30:21 CEST 2007
On 7/24/07, Ron Adam <rrr at ronadam.com> wrote:
> >> The same object in a class might look like...
> >> property foo(self):
> >> self.__value__ = None
> >> def __get__(self):
> >> return self.__value__
> >> def __set__(self, value):
> >> self.__value__ = value
> > In the first version, how is anything supposed to know that
> > the __value__ inside the function is an implicit attribute
> > of self rather than a local variable of the function
> In the first example self isn't implicit, it's non-existent. It would
> more like a generator that yields it value on gets, and receives its value
> on sets.
> In the second version self is passed to the functions explicitly so it can
> work in an instance. But other than that it's the same. It could also
> keep state between calls, in which case all instances of that class would
> share those values. (just like instances share class attributes)
> class bar(object):
> property foo(self):
> countgets = 0
> self.__value__ = None
> def __get__()
> countgets += 1
> return countgets, self.__value__
> def __set__(value)
> self.__value__ = value
> In this case countgets will be the total gets of all subclasses of bar.
> This could be done with a class attribute as well, but that breaks the
> of having a single self contained component. Having self contained
> components is more conducive to a modular design where you can more easily
> reuse parts.
Pardon me for interrupting... Don't the existing descriptors do all of this,
with almost exactly the same syntax? You just have to set a class variable
to an instance of the descriptor class, which is one extra line of code.
Additionally, this allows reuse of a descriptor class for multiple
properties, which as-far-as-I-can-tell your models don't.
Perhaps I'm missing something, but I can't see the actual benefit of your
suggestions (besides inline-ing of properties' names).
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