AFAIK ElementTree does not support XPath. Has it changed?
Anyway, you can use lxml and the following XPath expression:
import lxml.etree
doc = lxml.etree.parse('t.xml')
print doc.xpath('//element[text()="A"]')[0].text
print doc.xpath('//element[text()="A"]')[0].tag
The result will be:
A
element