#!/usr/bin/env python

import elementtree.ElementTree as ET
import sys

tree = ET.parse(sys.stdin)

# if you need the root element, use getroot
root = tree.getroot()

# the tree root is the toplevel element
for elem in root.findall('item/partno'):
    elem.text = 'x' + elem.text
    print 'Part Number is ' + elem.text
            
# ...manipulate tree...

tree.write("out.xml")