Another fun thing to try:
import lxml.etree
root = lxml.etree.fromstring('<root><element/><element/></root>') e1, e2= root[0], root[1]
e1.append(e2) e2.addnext(e1)
Result: infinite loop.
Another fun thing to try:
import lxml.etree
root = lxml.etree. fromstring( '<root> <element/ ><element/ ></root> ')
e1, e2= root[0], root[1]
e1.append(e2)
e2.addnext(e1)
Result: infinite loop.