from lxml import etree
import csv

ns = '{urn:schemas-microsoft-com:office:spreadsheet}'

doc = etree.parse('/home/share/guillaume/grid1_1cz1rlvt.xml')
tree = doc.getroot()

with open("output.csv", "w") as fh:
    csvwriter = csv.writer(fh)
    for row in tree.findall(".//{0}Row".format(ns)):
        csvwriter.writerow([cell.findtext('{0}Data'.format(ns)) for cell in row])