tree data structure

[Padraig Brady]

Duncan Booth wrote:
> Padraig Brady <Padraig at Linux.ie> wrote in 
> news:FM0e9.2860$cP3.6165 at news.iol.ie:
> 
> 
>>Hi,
>>
>>I've a graph like stucture represented
>>by a list of tuples:
>>
>>[(L0,S2), (S2,S0), (S2,S1), (S1,Q2), (S0,Q1), (S2,S3)]
>>
>>And would like to convert it to
>>a tree structure like:
>>
>>           S0 - Q1
>>         /
>>L0 - S2 - S3
>>         \
>>           S1 - Q2
>>
>>Any tips appreciated.
>>
> 
> Does this help?
> 
> data = [('L0', 'S2'), ('S2', 'S0'), ('S2', 'S1'), ('S1', 'Q2'), ('S0', 
> 'Q1'), ('S2', 'S3')]
> 
> # Produce a tuple where each node contains its name
> # and a list of its child nodes:
> #  (node, [child1, ...])
> nodes = {}
> for parent, child in data:
>     nodes.setdefault(parent, (parent, 
> []))[1].append(nodes.setdefault(child, (child, [])))
> 
> result = nodes[data[0][0]]
> 
> assert result==('L0', [('S2', [('S0', [('Q1', [])]), ('S1', [('Q2', [])]), 
> ('S3', [])])])
> 
> 

It certainly does!
Just one thing...Why use lists instead of tuples?

thanks,
Pádraig.

p.s. I am completely amazed by Python. What is it now.. 4 hours
and 43 minutes and I've learnt Python enough (from the web docs)
to be able to parse a "graph format" text file and outputting XML
(albeit with a little help :-)). Fantastic!