trees, iterations and adding leaves

[Gabriel Genellina]

At Sunday 31/12/2006 14:25, vertigo wrote:

>I use nltk package - but it should not matter here.

Yes, it does. The framework should provide some form of tree traversal.

>So i wanted to 'travel thru my tree' to last node which should be changed:
> >>> tree6 = Tree('main', ['sub1', 'sub2'])
> >>> subtree = tree6[0]
> >>> subtree
>'sub1'
> >>> subtree = Tree('newsub',[])
> >>> subtree
>('newsub': )
> >>> tree6
>('main': 'sub1' 'sub2')
>The problem is that subtree is some kind of a new variable (not pointer)
>so changing it i will not alter tree6.

This, yes, is a general Python question. When you bind something to 
the name "subtree", it doesn't matter what were "subtree" pointing to 
before. Read http://effbot.org/zone/python-objects.htm

>How to alter tree6 while
>'travelling along it's nodes',
>without messy referencing as tree6[0][1][0][1][1][1][0].......... ?

Without any further knowledge of the Tree objects, you could do 
something like this:

def traverse_tree(tree, *ids):
     result = tree
     while ids:
         key = ids.pop(0)
         tree = tree[key]
     return tree

and say: traverse_tree(tree6, 0, 1, 0, 1, 1, 1, 0) or 
traverse_tree(tree6, *[0,1,0,1,1,1,0]) or traverse_tree(tree6, 
*[0,1,0,1,1])[0] = another_object


-- 
Gabriel Genellina
Softlab SRL 


	

	
		
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