One Python 2.1 idea

[Moshe Zadka]

On Thu, 28 Dec 2000, "Alex Martelli" <aleaxit at yahoo.com> wrote:

> Now, I find out that, for that one instance only, I want to
> override the normal Ogre.foo method with another function
> which I also happen to have around:
> 
> def fun(self):
>     print 'have fun!'
> 
> 
> What are the 'good Pythonic ways' to do this, as opposed to
> 'dirty tricks'?  It seemed to me that, say:
> 
>     x.foo = new.instancemethod(fun, x, Ogre)
> 
> might be simpler and clearer than some alternative such as:
> 
>     x.__class__ = new.classobj('NewOgre', (Ogre,), {'foo':fun})

Personally, I avoid the ``new'' module completely (last I checked,
it wasn't portable to Jython, and it's all around tricky).

I'd simply do:

class _temp(Ogre):
	foo = fun
x.__class__ = _temp

Sometimes even encapsulating it in a function:

def add_method_to_instance(instance, name, function):
	class _temp(instance.__class__):
		pass
	setattr(_temp, name, function)
	instance.__class__ = _temp

One additional benefit of the __class__ method is that it is
honest: you change the class when you changed the methods,
because behaviour *has* changed.

-- 
Moshe Zadka <sig at zadka.site.co.il>
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