How to inheritance overwrite non virtual?

[Axel Straschil]

Hi!

I've got an class with a couple of depending methods.
I want to inheritance and create a new class where just
one method ist overwritten.

My problem: When python is executing the mother-method,
not the depending mother-method is taken, it take the
method of the chield.

In my example, i want that K2.bestCaptionl ong() returns
the same as KObject.bestCap tionlong() - no way!

I've tryed (in K2) something like:
def bestCaptionlong (self):
return KObject().bestC aptionlong()
which I expected to be like KObject::bestCa ptionlong() in
C++, but it doesn't work ;-(

Any Idea how to make the mother-class calling her method's?

Here is my Example:

class KObject:
def __init__(self):
self._label=Non e
self._caption=N one
self._captionlo ng=None
def __str__(self):
return (
"label: [%s], %s, (%s)\n"+
"caption: [%s], %s, (%s)\n"+
"captionlon g: [%s], %s, (%s)"
)%( self._label, self.label(), self.bestLabel( ),
self._caption, self.caption(), self.bestCaptio n(),
self._captionlo ng, self.captionlon g(), self.bestCaptio nlong()
)
def label(self):
return self._label
def caption(self):
return self._caption
def captionlong(sel f):
return self._captionlo ng
def bestLabel(self) :
return self.label()
def bestCaption(sel f):
if self.caption() is not None:
return self.caption()
else:
return self.bestLabel( )
def bestCaptionlong (self):
if self.captionlon g() is not None:
return self.captionlon g()
else:
return self.bestCaptio n()

class K2(KObject):
def bestCaption(sel f):
return "Overwritte n"

k = KObject()
k._label='x'

k2 = K2()
k2._label='x'

print k
print k2

Thanks, AXEL.

[Peter Otten]

Re: How to inheritance overwrite non virtual?

Axel Straschil wrote:
[color=blue]
> I've tryed (in K2) something like:
> def bestCaptionlong (self):
> return KObject().bestC aptionlong()
> which I expected to be like KObject::bestCa ptionlong() in
> C++, but it doesn't work ;-([/color]

The following will do:

class Derived(Base):
def method(self):
return Base.method(sel f) # call base class method

(Of course you need not override the method if the body of the derived class
only calls the base class method.)

Peter

[Axel Straschil]

Re: How to inheritance overwrite non virtual?

Hi!
[color=blue]
> The following will do:
>
> class Derived(Base):
> def method(self):
> return Base.method(sel f) # call base class method[/color]

I tried in my chield-class:
class K2(KObject):
def bestCaption(sel f):
return "Overwritte n"
def bestCaptionlong (self):
return KObject.bestCap tionlong(self)

The Problem ist inside of KObject.bestCap tionlong(self):
return self.bestCaptio n()

The mother-class is calling the method of the child-class, not
it own method. I want the mother-method to be called like "the
chield never was existing", but I find no way.

Anny other idea?

Thank, AXEL.

[anton muhin]

Re: How to inheritance overwrite non virtual?

Axel Straschil wrote:
[color=blue]
> Hi!
>
>[color=green]
>>The following will do:
>>
>>class Derived(Base):
>> def method(self):
>> return Base.method(sel f) # call base class method[/color]
>
>
> I tried in my chield-class:
> class K2(KObject):
> def bestCaption(sel f):
> return "Overwritte n"
> def bestCaptionlong (self):
> return KObject.bestCap tionlong(self)
>
> The Problem ist inside of KObject.bestCap tionlong(self):
> return self.bestCaptio n()
>
> The mother-class is calling the method of the child-class, not
> it own method. I want the mother-method to be called like "the
> chield never was existing", but I find no way.
>
> Anny other idea?
>
> Thank, AXEL.[/color]

Change
return self.bestCaptio n()

to
return KObject.bestCap tion(self)

hth,
anton.

[Peter Otten]

Re: How to inheritance overwrite non virtual?

Axel Straschil wrote:
[color=blue]
> Hi!
>[color=green]
>> The following will do:
>>
>> class Derived(Base):
>> def method(self):
>> return Base.method(sel f) # call base class method[/color]
>
> I tried in my chield-class:
> class K2(KObject):
> def bestCaption(sel f):
> return "Overwritte n"
> def bestCaptionlong (self):
> return KObject.bestCap tionlong(self)
>
> The Problem ist inside of KObject.bestCap tionlong(self):
> return self.bestCaptio n()
>
> The mother-class is calling the method of the child-class, not
> it own method. I want the mother-method to be called like "the
> chield never was existing", but I find no way.
>
> Anny other idea?
>
> Thank, AXEL.[/color]

What you want seems to be

class KObject:
def bestCaptionlong (self):
# class made explicit to guard against overriding
return KObject.bestCap tion(self)

Some additional remarks:
Do-nothing accessor methods may be acceptable style in C++ but are
superfluous in Python.
The abundance of xxxCaption and label attributes somewhat obscures your
design goal for me, but usually the ability to override a method to change
its effect is a feature, not something to fight against.

Peter




Peter

[Richie Hindle]

Re: How to inheritance overwrite non virtual?


[Axel][color=blue]
> The mother-class is calling the method of the child-class, not
> it own method. I want the mother-method to be called like "the
> chield never was existing", but I find no way.[/color]

class A:
def bwahHaHa(self):
"""When called by callMe(), derived classes don't get a look in."""
print "Bwah-Ha-Ha!"

def callMe(self):
"""Calls non-overridable method bwahHaHa()."""
A.bwahHaHa(self ) ########## This is the interesting bit ##########

class B(A):
def bwahHaHa(self):
"""Vain attempt to override what callMe() does."""
print "Squeak"

b = B()
b.callMe() # Prints "Bwah-Ha-Ha!"
b.bwahHaHa() # Prints "Squeak"

--
Richie Hindle
richie@entrian. com

[Axel Straschil]

Re: How to inheritance overwrite non virtual?

Hello!
[color=blue]
> What you want seems to be
> class KObject:
> def bestCaptionlong (self):
> # class made explicit to guard against overriding
> return KObject.bestCap tion(self)
>[/color]

Yes, that behaves the way I excpected, thank's to you and the other
for helping me!
[color=blue]
> Do-nothing accessor methods may be acceptable style in C++ but are
> superfluous in Python.[/color]

I'm afraid I'm still not thinking in python, I'll work on it ;-)

Lg, AXEL.