Prototyping 21 May 2013

• Tree
• Walking a tree
• Recursive traversal
• Depth-first traversal
• Breadth-first traversal

ElementTree

http://docs.python.org/2/library/xml.etree.elementtree.html

Tree Traversal

http://en.wikipedia.org/wiki/Tree_traversal

File:Sorted binary tree preorder.svg500px

http://localhost/doc/python2.7/html/library/xml.etree.elementtree.html?highlight=element#xml.etree.ElementTree

Walking the tree

ElementTree the fundamental unit is the Element

And Element has:

• .tag (a string representing the name of the tag, like "p" or "script")
• .attrib (a "dictionary" with name=value pairs of the tag attributes, like id="foo", or style="color: blue")
• .text (String of text contents of the node)
• .tail (if there's text after child tags, it'd be here)

In addition (and this is why it's a tree), each element can be iterated / treated like a list of all sub-elements.

• Iteration to access contained "child" elements

Walk

def walk (node):
    print node.tag
    for child in node:
        walk(child)

Extracting the text of a node

(function exists?)

How to show the structure in a more tree way?

center... breadth first traversal!

Cherry picking

(collecting things while walking the tree)