[XML-SIG] New to Python OO

[Andrew M. Kuchling]

Michael Sanborn writes:
>imports xml.dom.core and xml.dom.builder. I would have thought that the
>way to approach this would be to define a local Node class derived from
>core.py that added an empty totxt() method, and then to define local
>subclasses of Node (such as Text) with specific totxt() methods. 

	Things aren't that simple, because of the implementation,
which consists of a tree of hidden objects; the classes that you
interact with, such as Node, Element, Text, etc. are all proxies for
that hidden tree, and create new Node, Element, Text, ... proxies when 
you request a new portion.  So all the retrieval methods would have to 
be aware 
	
>My
>reasoning was that the Builder class would then build the tree with my
>enhanced Nodes. But that doesn't seem to be happening. Instead, Builder
>seems to be constructing the tree with regular core Nodes that don't
>recognize my totxt() method. Can anyone give me advice on how to achieve
>this?

	My suspicion is that subclassing Node classes isn't the way to
go; instead, you'll write functions and classes (probably using
existing classes such as Builder and Walker) that operate on DOM
trees.  However I'd really like to see a discussion of this.  We need
to work out common Python/DOM patterns, so that we can add appropriate
helper modules and functions.  (They'll also be useful to document as
examples.)

-- 
A.M. Kuchling			http://starship.skyport.net/crew/amk/
The multiple human needs and desires that demand privacy among two or more
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men thrive and wherever they write.
    -- David Kahn, _The Codebreakers_