Extending a class on runtime

[rdaunoravicius]

Hi,

Let's say you have a bunch of instatiated objects of the same class on
your hands and you want to had some functionality to them.

I'm facing this situation while working with PyGTK and libglade to
create a GUI. Libglade creates a whole object tree representing the
GUI out of an XML file, and a bunch of GtkComboBox objects are
instantiated. I don't like the way GtkComboBox objects works, so I'd
like them to have some extra methods. Inheriting and extending
GtkComboBox is pointless because I'm not the one instantiating the
class. I only came up with three possibilities:

A) Adding my methods to the objects in a for-loop

B) Adding my methods to the GtkComboBox class (I tried this and it
seems to work)

C) Create a GtkComboBoxExtended class inheriting from GtkComboBox
and change the instances' class in a for-loop.

I'm kind of inclined to C. B sounds dangerous and A is plain ugly.
I'm very new to this and I'm sure there is a well-established pythonic
way to solve this problem, so I'm appealing for your vast collective
wisdom to point me in the path of righteousness.

Thanks,
Rodrigo

 

[Bruno Desthuilliers]

(e-mail address removed) a écrit :

Hi,

Let's say you have a bunch of instatiated objects of the same class on
your hands and you want to had some functionality to them.

Then I'd just do it.

I'm facing this situation while working with PyGTK and libglade to
create a GUI. Libglade creates a whole object tree representing the
GUI out of an XML file, and a bunch of GtkComboBox objects are
instantiated. I don't like the way GtkComboBox objects works, so I'd
like them to have some extra methods. Inheriting and extending
GtkComboBox is pointless because I'm not the one instantiating the
class. I only came up with three possibilities:

A) Adding my methods to the objects in a for-loop

B) Adding my methods to the GtkComboBox class (I tried this and it
seems to work)

I don't have much experience with PyGTK, but unless GtkComboBox is a
very special class object, it should JustWork(tm).

C) Create a GtkComboBoxExtended class inheriting from GtkComboBox
and change the instances' class in a for-loop.

That's another possible solution, but it requires more work.

I'm kind of inclined to C. B sounds dangerous

Why ? Eventually confusing if not well documented, but mostly harmless
IMHO. Python is dynamic by nature, and there's no reason to not take
advantage of this fact.

and A is plain ugly.

It's also the more complicated and less efficient solution IMHO (unless
you want different implementations of the same method on a per-instance
basis...).

I'm very new to this and I'm sure there is a well-established pythonic
way to solve this problem, so I'm appealing for your vast collective
wisdom to point me in the path of righteousness.

As far as I'm concerned, and if it's just a matter of adding a couple of
methods, I'd go for B, which is the SimplestThingToDo(tm).

Now if it's a big complicated project with a rather unstable team, C is
perhaps a bit more explicit since it makes obvious that this not a
pristine GtkComboBox no more. But even then, it's always possible to
monkeypatch a class in a more or less documented way (explict mentions
of the patch in added/replaced/extended methods and in __repr__()).

My 2 cents...