Python: traverse tree adding html list (ul)

Question

I have this python code that will traverse a tree structure. I am trying to add ul and li tags to the function but I am not very succesful. I though I was able to keep the code clean without to many conditionals but now I ain't so sure anymore.

def findNodes(nodes):

    def traverse(ns):
        for child in ns:
            traverse.level += 1
            traverse(child.Children)
            traverse.level -= 1

    traverse.level = 1
    traverse(nodes)

This is the base function I have for traversing my tree structure. The end result should be nested ul and li tags. If need I can post my own not working examples but they might be a little confusing.

Update: Example with parameter

def findNodes(nodes):

    def traverse(ns, level):
        for child in ns:
            level += 1
            traverse(child.Children, level)
            level -= 1

    traverse(nodes, 1)

Since you're using recursion anyway, why not make level a parameter to traverse too? — kennytm
– kennytm, Commented Aug 13, 2010 at 7:17
Ah, that's a good idea. I got the code from Google and traverse.level was always a little fuzzy to me. I'll add a example with a parameter. — Pickels
– Pickels, Commented Aug 13, 2010 at 7:27

habnabit · Accepted Answer · 2010-08-13 07:44:45Z

2

I removed the unused level parameter. Adding in any sort of text is left as an exercise to the reader.

def findNodes(nodes):
    def traverse(ns):
        if not ns:
            return ''

        ret = ['<ul>']
        for child in ns:
            ret.extend(['<li>', traverse(child.Children), '</li>'])
        ret.append('</ul>')
        return ''.join(ret)

    return traverse(nodes)

edited Aug 13, 2010 at 7:44

answered Aug 13, 2010 at 7:29

habnabit

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3 Comments

Pickels Over a year ago

Thanks, that looks really good. But doesn't it leave me with an empty <ul> if there are no children?

habnabit Over a year ago

I fixed it, if you really care about that.

Pickels Over a year ago

I really liked your answer. Thanks again!

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