Re: Pb with descriptor and super ...
On Mar 9, 11:22 am, Erwan Adam <[EMAIL PROTECTED]> wrote: [snip] > > [EMAIL PROTECTED] /home/adam/Work/Python]> python super_from_guido.py > Using built-in super > Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c> > and typ is > Using python Super > Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c> > and typ is None > Using python MySuper > Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c> > and typ is It seems to me that it is the built-in super which has the correct behaviour. When you write obj.attr, python calls attr.__get__(obj, type(obj)) and not attr.__get__(obj) which sets the second arg to None. You can check this by creating a barebone descriptor that simply prints its arguments: class D(object): def __get__(self, obj, objtype): print obj, objtype class A(object): d=D() A().d <__main__.A object at 0x133c5f0> # objtype is not None! Therefore in your case when you do super(B, b).attr then A.__dict__['attr'].__get__(b, type(b)) is called. You can try this, it should give the same output as builtin super. > the Super gives None for typ ... which is quite surprising ! > In MySuper, I just change > > x = x.__get__(self.__obj__) > > by > > x = x.__get__(self.__obj__, cls) > at the -3 :) line of the class ... and it gives the result I expected > at the beginning : obj is b and typ is A Neither of these are right I think. If my explanation above is right the correct line should be: x = x.__get__(self.__obj__, type(self.__obj__)) HTH -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: Pb with descriptor and super ...
En Fri, 09 Mar 2007 08:22:46 -0300, Erwan Adam <[EMAIL PROTECTED]> escribió: > Thanks for your answer ... I followed the link > and tried to use the "fully functional implementation of > the super() built-in class in pure Python" given > on this page and the result is quite surprising : It appears that there is some disagreement on how the super object should behave. If you want to know what it actually *does* now (not what it *should* do) you can look at typeobject.c, but it's a bit hard to read, and I don't understand it in full... Maybe looking at the test suite is easier, in test_descr.py -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Pb with descriptor and super ...
Gabriel Genellina a écrit :
> En Fri, 09 Mar 2007 06:25:08 -0300, Erwan Adam <[EMAIL PROTECTED]>
> escribió:
>
>> I have a problem with the use of descriptors
>> and super. The file is :
>
> Descriptors for "super" behave a bit different than for classes. See
> http://www.python.org/2.2/descrintro.html#cooperation
>
> --Gabriel Genellina
>
Hi Gabriel,
Thanks for your answer ... I followed the link
and tried to use the "fully functional implementation of
the super() built-in class in pure Python" given
on this page and the result is quite surprising :
# -
class Super(object):
def __init__(self, type, obj=None):
self.__type__ = type
self.__obj__ = obj
def __get__(self, obj, type=None):
if self.__obj__ is None and obj is not None:
return Super(self.__type__, obj)
else:
return self
def __getattr__(self, attr):
if isinstance(self.__obj__, self.__type__):
starttype = self.__obj__.__class__
else:
starttype = self.__obj__
mro = iter(starttype.__mro__)
for cls in mro:
if cls is self.__type__:
break
# Note: mro is an iterator, so the second loop
# picks up where the first one left off!
for cls in mro:
if attr in cls.__dict__:
x = cls.__dict__[attr]
if hasattr(x, "__get__"):
x = x.__get__(self.__obj__)
return x
raise AttributeError, attr
class Desc(object):
def __init__(self, class_name):
self.class_name = class_name
return
def __get__(self, obj, typ=None):
print "Desc.__get__ : class_name is %s, obj is %s and typ is
%s"%(self.class_name, obj, typ)
return
pass
class A(object):
attr = Desc("A")
pass
class B(A):
attr = Desc("B")
pass
b = B()
print "Using built-in super"
attr = super(B, b).attr
print "Using python Super"
attr = Super(B, b).attr
class MySuper(object):
def __init__(self, type, obj=None):
self.__type__ = type
self.__obj__ = obj
def __get__(self, obj, type=None):
if self.__obj__ is None and obj is not None:
return Super(self.__type__, obj)
else:
return self
def __getattr__(self, attr):
if isinstance(self.__obj__, self.__type__):
starttype = self.__obj__.__class__
else:
starttype = self.__obj__
mro = iter(starttype.__mro__)
for cls in mro:
if cls is self.__type__:
break
# Note: mro is an iterator, so the second loop
# picks up where the first one left off!
for cls in mro:
if attr in cls.__dict__:
x = cls.__dict__[attr]
if hasattr(x, "__get__"):
x = x.__get__(self.__obj__, cls)
return x
raise AttributeError, attr
print "Using python MySuper"
attr = MySuper(B, b).attr
# --
it gives :
[EMAIL PROTECTED] /home/adam/Work/Python]> python super_from_guido.py
Using built-in super
Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c>
and typ is
Using python Super
Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c>
and typ is None
Using python MySuper
Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7bc302c>
and typ is
the Super gives None for typ ... which is quite surprising !
In MySuper, I just change
x = x.__get__(self.__obj__)
by
x = x.__get__(self.__obj__, cls)
at the -3 :) line of the class ... and it gives the result I expected
at the beginning : obj is b and typ is A
Best regards,
E.A.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Pb with descriptor and super ...
Erwan Adam a écrit :
> Hi all,
>
> I have a problem with the use of descriptors
> and super. The file is :
>
> # ---
>
> class Desc(object):
> def __init__(self, class_name):
> self.class_name = class_name
> return
> def __get__(self, obj, typ):
> print "Desc.__get__ : class_name is %s, obj is %s and typ is
> %s"%(self.class_name, obj, typ)
> return
> pass
>
> class A(object):
> attr = Desc("A")
> pass
>
> class B(A):
> attr = Desc("B")
> pass
>
> b = B()
>
> print "---"
> print "Getting b.attr ..."
> print "I hope that : class_name is B, obj is b and typ is B"
> b.attr
> print "---"
> print "Getting super(B, b).attr ..."
> print "I hope that : class_name is A, obj is b and typ is A but it is
> not the case !"
> super(B, b).attr
> print "---"
>
> # ---
>
> and the result is :
>
> ---
> Getting b.attr ...
> I hope that : class_name is B, obj is b and typ is B
> Desc.__get__ : class_name is B, obj is <__main__.B object at 0xb7b1f8ec>
> and typ is
> ---
> Getting super(B, b).attr ...
> I hope that : class_name is A, obj is b and typ is A but it is not the
> case !
> Desc.__get__ : class_name is A, obj is <__main__.B object at 0xb7b1f8ec>
> and typ is
> ---
>
> I expected that when getting super(B, b).attr, typ is A, but it is not
> the case ...
Moreover, on the page :
http://users.rcn.com/python/download/Descriptor.htm
the author writes :
"The call super(B, obj).m() searches obj.__class__.__mro__ for the base
class A immediately following B and then returns
A.__dict__['m'].__get__(obj, A)."
which it seems not the case ...
Is it a bug or a mis-understood ?
Regards,
E.A.
>
> python used :
>
> [EMAIL PROTECTED] /home/adam/Work/Python]> python
> Python 2.4.3 (#2, Sep 18 2006, 21:07:35)
> [GCC 4.1.1 20060724 (prerelease) (4.1.1-3mdk)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> >>>
>
>
> Best regards,
>
>
> E.A.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Pb with descriptor and super ...
En Fri, 09 Mar 2007 06:25:08 -0300, Erwan Adam <[EMAIL PROTECTED]> escribió: > I have a problem with the use of descriptors > and super. The file is : Descriptors for "super" behave a bit different than for classes. See http://www.python.org/2.2/descrintro.html#cooperation -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
