# XML "function" nodes that evaluate their contents to text

import xml_dom

def map_items(func, items):

    return [(name, func(value)) for name, value in items]

def range_(items):

    items = dict(map_items(float, items))

    return str(items['to'] - items['from'])

def avg(items):

    count = 0

    sum_ = 0.

    for name, value in map_items(float, items):

        count += 1

        sum_ += value

    return str(sum_/count)

def date(items):

    items = dict(items)

    return '-'.join([items['year'], items.get('month', '1'),

        items.get('day', '1')])

# Function names must start with _ to avoid collisions with real tags

# Functions have take arguments (doc, node)

funcs = {'_range': range_, '_avg': avg, '_date': date}

def process(doc, node=None):

    if node == None: node = doc.documentElement

    name = xml_dom.name_of(node)

    if name in funcs: xml_dom.replace_with_text(doc, node,

        funcs[name](xml_dom.NodeTextEntryIter(node)))

    else:

        for child in xml_dom.NodeElemIter(node): process(doc, child)