xml.etree.ElementTree get node depth

Question

The XML:

<?xml version="1.0"?>
<pages>
    <page>
        <url>http://example.com/Labs</url>
        <title>Labs</title>
        <subpages>
            <page>
                <url>http://example.com/Labs/Email</url>
                <title>Email</title>
                <subpages>
                    <page/>
                    <url>http://example.com/Labs/Email/How_to</url>
                    <title>How-To</title>
                </subpages>
            </page>
            <page>
                <url>http://example.com/Labs/Social</url>
                <title>Social</title>
            </page>
        </subpages>
    </page>
    <page>
        <url>http://example.com/Tests</url>
        <title>Tests</title>
        <subpages>
            <page>
                <url>http://example.com/Tests/Email</url>
                <title>Email</title>
                <subpages>
                    <page/>
                    <url>http://example.com/Tests/Email/How_to</url>
                    <title>How-To</title>
                </subpages>
            </page>
            <page>
                <url>http://example.com/Tests/Social</url>
                <title>Social</title>
            </page>
        </subpages>
    </page>
</pages>

The code:

// rexml is the XML string read from a URL
from xml.etree import ElementTree as ET
tree = ET.fromstring(rexml)
for node in tree.iter('page'):
    for url in node.iterfind('url'):
        print url.text
    for title in node.iterfind('title'):
        print title.text.encode("utf-8")
    print '-' * 30

The output:

http://example.com/article1
Article1
------------------------------
http://example.com/article1/subarticle1
SubArticle1
------------------------------
http://example.com/article2
Article2
------------------------------
http://example.com/article3
Article3
------------------------------

The Xml represents a tree like structure of a sitemap.

I have been up and down the docs and Google all day and can't figure it out hot to get the node depth of entries.

I used counting of the children container but that only works for the first parent and then it breaks as I can't figure it out how to reset. But this is probably just a hackish idea.

The desired output:

0
http://example.com/article1
Article1
------------------------------
1
http://example.com/article1/subarticle1
SubArticle1
------------------------------
0
http://example.com/article2
Article2
------------------------------
0
http://example.com/article3
Article3
------------------------------

Answer 1

The Python ElementTree API provides iterators for depth-first traversal of a XML tree - unfortunately, those iterators don't provide any depth information to the caller.

But you can write a depth-first iterator that also returns the depth information for each element:

import xml.etree.ElementTree as ET

def depth_iter(element, tag=None):
    stack = []
    stack.append(iter([element]))
    while stack:
        e = next(stack[-1], None)
        if e == None:
            stack.pop()
        else:
            stack.append(iter(e))
            if tag == None or e.tag == tag:
                yield (e, len(stack) - 1)

Note that this is more efficient than determining the depth via following the parent links (when using lxml) - i.e. it is O(n) vs. O(n log n).