On Jul 23, 7:19 am, DG <dang...@gmail.com> wrote:
> On Jul 22, 6:05 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar>
> wrote:
>
>
>
> > En Wed, 22 Jul 2009 11:01:09 -0300, Rhodri James
> > <rho...@wildebst.demon.co.uk> escribió:
>
> > > On Wed, 22 Jul 2009 06:02:55 +0100, Gabriel Genellina
> > > <gagsl-...@yahoo.com.ar> wrote:
>
> > >> class X(object):
> > >> foo = descriptor()
>
> > >> x = X()
> > >> x.foo = "value"
>
> > > Isn't this going to create a brand new instance attribute x.foo that has
> > > nothing to do with the descriptor anyway?
>
> > No, it's up to the descriptor __set__ method what happens in this case.
> > Think of the standard 'property' descriptor, the fset function can do
> > whatever it wants.
> > Also, a data descriptor takes precedence over any instance attribute of
> > the same name that might exist.
>
> > --
> > Gabriel Genellin
>
> You might've already thought of this (and it is annoying), but you
> could pass the name through the descriptor's init method. I believe
> this is the only way besides assigning a metaclass that will look for
> that type of descriptor upon class creation and set the descriptor's
> name at that time.
>
> class A(object):
> def __init__(self, attr_name):
> self._name = attr_name
> def __set__(self, instance, value):
> self.instance.__dict__[self._name] = value
> # or something like that...
>
> class B(object):
> foo = A('foo')
Well of course I think of more alternatives after I post.
1) still annoying... pass the class through a 'registering' function
that will examine all of it's attrs and find the ones that are of your
descriptor type, and assign the attr_name upon that descriptor.name
attribute.
2) I just thought of, and it's kind of a hack is to do this
examination within the '__set__' method.
e.g.
class A(object):
def __get__(self, instance, owner):
if instance is None:
return self
else:
# do something different here for instances' access
return self
def __set__(self, instance, value):
cls = instance.__class__
name = None
for attr in dir(cls):
if getattr(cls, attr) is self:
name = attr
print name
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