Dynamic subclassing ?

James T. Dennis jadestar at idiom.com
Sun Jun 10 23:16:12 CEST 2007


Karlo Lozovina <_karlo_ at _mosor.net> wrote:
> 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(Button, 
> Button.__dict__.update(ExtensionClass.__dict__))

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

> Seems to do what you want it to do.

> HTH,
> Karlo.

 When I try something like this I run into a little problem:

	class Foo:
	    def foo(self):
	        return "foo"
	class Bar:
	    def bar(self):
	        return "bar"

	f = Foo()
	f.__dict__.update(Bar.__dict__)

 ... the problem is that while f now has a "bar" method it doesn't
 work quite like a normal instance method:

	>>> f.bar()
	Traceback (most recent call last):
	  File "<stdin>", line 1, in ?
	TypeError: bar() takes exactly 1 argument (0 given)
	>>> 

 ... though I can get by with f.bar(f)

 This "new" module seems to be the key to it all; but the only
 docs I have for that say:

>>> help(new)
Help on module new:

NAME
    new - Create new objects of various types.  Deprecated.

FILE
    /usr/lib/python2.4/new.py

MODULE DOCS
    http://www.python.org/doc/current/lib/module-new.html

DESCRIPTION
    This module is no longer required except for backward compatibility.
    Objects of most types can now be created by calling the type object.


 ... which sounds like a bad idea (from the word "Deprecated").








-- 
Jim Dennis,
Starshine: Signed, Sealed, Delivered




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