Velocity Reviews > super problem

# super problem

Uwe Mayer
Guest
Posts: n/a

 06-25-2005
Hi,

I have a diamond-shaped multiple inheritanc chain with new style classes,
but super() does not call the parent class correctly:

-- snip --
from qtcanvas import *

class B2(QCanvasItem):
def move(self, x,y):
super(B2, self).move(0,0)
print "B2"

class C2(QCanvasItem):
def move(self, x,y):
super(C2, self).move(0,0)
print "C2"

class D2(QCanvasPolygonalItem, B2, C2):
def move(self, x,y):
super(D2, self).move(0,0)
print "D2"

d2 = D2(None)
d2.move(0,0)
-- snip --
returns:

Traceback (most recent call last):
File "tmp.py", line 46, in ?
d2.move(0,0)
File "tmp.py", line 42, in move
super(D2, self).move(0,0)
File "tmp.py", line 32, in move
super(B2, self).move(0,0)
File "tmp.py", line 37, in move
super(C2, self).move(0,0)
AttributeError: 'super' object has no attribute 'move'

super(C2, self).move(0,0) should resolve to QCanvasItem.move
AFAIK super only works with new-style classes, so I checked:

>>> from qtcanvas import *
>>> isinstance(QCanvasItem, object)

True

A way to fix this is to introduce a dummy

class A2(QCanvasItem):
def move(self,x,y): QCanvasItem.move(self,x,y)

This is stupid, as it only delays execution by one intermediary call.

Is this a bug?

Thanks,
Ciao
Uwe

Michael Hoffman
Guest
Posts: n/a

 06-25-2005
Uwe Mayer wrote:

> I have a diamond-shaped multiple inheritanc chain with new style classes,
> but super() does not call the parent class correctly:
>
> -- snip --
> from qtcanvas import *

I don't have qtcanvas installed, and I couldn't reproduce the
undesirable behavior using a dummy class. If you try to create a
self-contained testcase, you will have an easier time figuring where the
problem is.
--
Michael Hoffman

Konstantin Veretennicov
Guest
Posts: n/a

 06-25-2005
On 6/25/05, Uwe Mayer <(E-Mail Removed)> wrote:
> AFAIK super only works with new-style classes, so I checked:
>
> >>> from qtcanvas import *
> >>> isinstance(QCanvasItem, object)

> True

AFAIK, this is not the right way to check for new-styledness:

>>> class X: "i'm an old-styler"
>>> isinstance(X(), object)

True

But this is:

>>> isinstance(X, type)

False

- kv