kedra marbun a écrit :
On Jul 7, 2:46 am, Bruno Desthuilliers
<bdesth.quelquech...@free.quelquepart.fr> wrote:
Gregory Ewing a écrit :
Bruno Desthuilliers wrote:
kedra marbun a écrit :
if we limit our discussion to py:
why __{get|set|delete}__ don't receive the 'name' & 'class' from
__{getattribute|{set|del}attr}__
'name' is the name that is searched
While it would have been technically possible, I fail to imagine any use
case for this.
I think he wants to have generic descriptors that are
shared between multiple attributes, but have them do
different things based on the attribute name.
I already understood this, but thanks !-)
What I dont understand is what problem it could solve that couldn't be
solved more simply using the either _getattr__ hook or hand-coded
delegation, since such a descriptor would be so tightly coupled to the
host class that it just doesn't make sense writing a descriptor for this.
yeah, i finally can agree descriptor isn't supposed to be used as
delegation in general, it should be the job of __getattr__
however i still think passing name would open up some other
possibilities of use
Nothing prevents you to pass a "name" to the descriptor instance when
instanciating it, ie:
class Desc(object):
def __init__(self, name):
self.name = name
def __get__(self, inst, cls):
# ...
def __set__(self, inst, value):
# ...
class Foo(object):
bar = Desc("bar")
baaz = Desc("baaz")
Ok, this is not necessarily what you were looking for, but it's IMHO
less brittle than relying on which attribute name was looked up (which
is something the descriptor shouldn't have to care about).
btw, is there a common approach to let the interface of a class that
uses __getattr__, to include names that are delegated?
In Python 2.x, not that I know (but it may have passed under my radar).
If what you want it to automate delegation of a set of methods without
too much manual coding, you can use a custom metaclass that will add the
relevant methods to the class, based on (ie) a list (or mapping) of
methods names. But that might be a bit overkill.
class A:
def do_this(self): ...
class B:
a = A()
I don't see the point of using delegation on a class attribute. That's
typically what inheritance is for.
def do_that(self): ...
def __getattr__(self, name):
try:
return types.MethodType(getattr(self.a, name), self)
Err... Did you try the simple way ?
return getattr(self.a, name)
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