design question: no new attributes

Diez B. Roggisch deets at
Thu Mar 1 23:58:57 CET 2007

> One last point. While I remain interested in examples of how
> "late" addition of attributes to class instances is useful,
> I must note that everyone who responded agreed that it
> has been a source of bugs.  This seems to argue against a
> general ban on "locking" objects in some way, in some
> circumstances.

I've got some examples. I quite often used dynamic attributes in 
situations where I wasn't the creator of certain objects, but had to use 
them and wanted to link them with my own code.

For example, in various GUI-environments, you've got some sort of tree 
view, usually containing item-objects that form the tree.

Now in other languages like C++ or Java, I have to subclass those items 
(if possible at all) if I want to associate my own data (for example the 
"real" object behind such an item) with them. Or I need to have an 
awkward global mapping between tree-items and my data.

But in python, I can just easily add a new .data_object property, and in 
whatever event-handler spits a e.g. selected item at me, I'm easily 
accessing the data behind it.

Other examples are processing XML-trees that also have associated data 
and the like.


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