simple example for parse gnucash xml by lxml

gistfile1.py

#!/usr/bin/python

from lxml import etree
import gzip

tree = etree.parse(gzip.open('personal.gnucash'))
root = tree.getroot()

for i in tree.xpath('//gnc:GncInvoice[invoice:id[text()="000003"]]',namespaces=root.nsmap):
    print(i.tag)