Use getpath
from ElementTree objects.
from lxml import etree
root = etree.fromstring('''
<foo><bar>Data</bar><bar><baz>data</baz>
<baz>data</baz></bar></foo>
''')
tree = etree.ElementTree(root)
for e in root.iter():
print(tree.getpath(e))
Prints
/foo
/foo/bar[1]
/foo/bar[2]
/foo/bar[2]/baz[1]
/foo/bar[2]/baz[2]