Dynamic subclassing ?

[manatlan]

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.
Help is welcome
thanx

[Bruno Desthuilliers]

manatlan a écrit :

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods.

You don't even need setattr() here, you can set the attributes directly.

But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

You don't necessarily need subclassing here. What you want is a typical
use case of the Decorator pattern:

class MoreMethods(obj ect):
def __init__(self, button):
self._button = button

def sayHello(self):
print "hello"

def __getattr__(sel f, name):
return getattr(self._b utton, name)

def __setattr__(sel f, name, value):
if name in dir(self._butto n):
setattr(self._b utton, name, value)
else:
object.__setatt r__(self, name, value)

b = MoreMethods(gtk .Button())
b.set_label("k" )
b.say_hello()

[manatlan]

On 12 mai, 17:00, Bruno Desthuilliers
<bdesth.quelque [e-mail] quepart.frwrote :

manatlan a écrit :

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods.

You don't even need setattr() here, you can set the attributes directly.

But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

You don't necessarily need subclassing here. What you want is a typical
use case of the Decorator pattern:

class MoreMethods(obj ect):
def __init__(self, button):
self._button = button

def sayHello(self):
print "hello"

def __getattr__(sel f, name):
return getattr(self._b utton, name)

def __setattr__(sel f, name, value):
if name in dir(self._butto n):
setattr(self._b utton, name, value)
else:
object.__setatt r__(self, name, value)

b = MoreMethods(gtk .Button())
b.set_label("k" )
b.say_hello()

except that "b" is not anymore a "gtk.Button ", but a "MoreMethod s"
instance ...
i'd like that "b" stay a "gtk.Button " ...

[Daniel Nogradi]

I've got an instance of a class, ex :

>
b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

How about:

class MoreMethods:
def sayHello(self):
print "hello"

class myButton( gtk.Button, MoreMethods ):
pass

b = myButton( )

isinstance( b, gtk.Button ) # True
b.sayHello( ) # "hello"
Daniel

[manatlan]

On 12 mai, 18:38, "Daniel Nogradi" <nogr...@gmail. comwrote:

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

How about:

class MoreMethods:
def sayHello(self):
print "hello"

class myButton( gtk.Button, MoreMethods ):
pass

b = myButton( )

isinstance( b, gtk.Button ) # True
b.sayHello( ) # "hello"

yes, but it needs to recreate an instance (of mybutton) ...
i can't do that, in my context.
The only things i've got is my instance "b" (which can be whatever
object).
i'd like to add methods/attributes to this instance, by adding a
heritage of another class.

Daniel

thanks

[Karlo Lozovina]

manatlan wrote:

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

It's somewhat easy, boot looks ugly to me. Maybe someone has a more
elegant solution:

In [6]: import new

In [13]: class Button:
....: def buttonFunc(self ):
....: pass

In [14]: class ExtensionClass:
....: def extendedMethod( self):
....: pass

In [15]: hybrid = new.instance(Bu tton,
Button.__dict__ .update(Extensi onClass.__dict_ _))

In [17]: dir(hybrid)
Out[17]: ['__doc__', '__module__', 'buttonFunc', 'extendedMethod ']

Seems to do what you want it to do.

HTH,
Karlo.

[Daniel Nogradi]

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

How about:

class MoreMethods:
def sayHello(self):
print "hello"

class myButton( gtk.Button, MoreMethods ):
pass

b = myButton( )

isinstance( b, gtk.Button ) # True
b.sayHello( ) # "hello"

yes, but it needs to recreate an instance (of mybutton) ...
i can't do that, in my context.
The only things i've got is my instance "b" (which can be whatever
object).
i'd like to add methods/attributes to this instance, by adding a
heritage of another class.

I think that is not possible, at least in a simple way (there might be
a complicated way of messing with the MRO). Please anyone correct me
if I was wrong.

Daniel

[Steven Bethard]

manatlan wrote:

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

You can simply bind the methods you want to add to the Button instance.
That means doing the equivalent of ``b.sayHello = sayHello.__get_ _(b)``.
For example::

>>class Button(object):

... def set_label(self, label):
... print 'setting label:', label
...

>>def add_methods(obj , cls):

... for name, value in cls.__dict__.it ems():
... if callable(value) and hasattr(value, '__get__'):
... setattr(obj, name, value.__get__(o bj, type(obj)))
...

>>b = Button()
b.set_label(' k')

setting label: k

>>b.say_hello ()

Traceback (most recent call last):
File "<interacti ve input>", line 1, in <module>
AttributeError: 'Button' object has no attribute 'say_hello'

>>class MoreMethods(obj ect):

... def say_hello(self) :
... print 'hello'
...

>>add_methods(b , MoreMethods)
b.set_label(' m')

setting label: m

>>b.say_hello ()

hello

HTH,

STeVe

[Alex Martelli]

manatlan <ma******@gmail .comwrote:

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

I think what you're asking for is totally weird, and with just about
zero advantages compared with several saner alternatives that have
already been proposed in this thread and that you have rejects, but
sure, it's possible:

def addaclass(anins t, onemoreclass):
aninst.__class_ _ = type(aninst.__a class__.__name_ _,
(aninst.__aclas s__, onemoreclass), {})
Alex

[manatlan]

On 13 mai, 01:24, [e-mail] (Alex Martelli) wrote:

manatlan <manat...@gmail .comwrote:

I've got an instance of a class, ex :

b=gtk.Button()

I'd like to add methods and attributes to my instance "b".
I know it's possible by hacking "b" with setattr() methods. But i'd
like to do it with inheritance, a kind of "dynamic subclassing",
without subclassing the class, only this instance "b" !

In fact, i've got my instance "b", and another class "MoreMethod s"

class MoreMethods:
def sayHello(self):
print "hello"

How could i write ...

"b = b + MoreMethods"

so "b" will continue to be a gtk.Button, + methods/attributs of
MoreMethods (it's what i call "dynamic inheritance") ...so, things
like this should work :

- b.set_label("k" )
- b.sayHello()

I can't find the trick, but i'm pretty sure it's possible in an easy
way.

I think what you're asking for is totally weird, and with just about
zero advantages compared with several saner alternatives that have
already been proposed in this thread and that you have rejects, but
sure, it's possible:

def addaclass(anins t, onemoreclass):
aninst.__class_ _ = type(aninst.__a class__.__name_ _,
(aninst.__aclas s__, onemoreclass), {})

Alex

I know it's weird ... and solutions given here are a lot saner. But i
can't do that at the creation of the instance, because it's not me who
has the creation process ... the only things i've got, it's the
instance

i tried :

class MoreMethods:
def sayHello(self):
print "hello"

def addaclass(anins t, onemoreclass):
aninst.__class_ _ = type(aninst.__c lass__.__name__ ,
(aninst.__class __, onemoreclass), {})

b=gtk.Button("t he_label")
addaclass(b,Mor eMethods)
print b.get_label()
print b.hello()

but got :
"TypeError: __class__ assignment: only for heap types"
on the last line ...

I begin to think that the only solution is to use the module new like
Karlo said ...