Get html DOM tree by only basic builtin moudles

[Laura Creighton]

Elementtree is part of the Python standard library.  You are better off
using it than rolling your own.   (If you were one of the rare people who
have some very strange requirements that make you better off writing your
own, you wouldn't be asking us.  You'd already know.)

https://docs.python.org/2.7/library/xml.etree.elementtree.html#module-xml.etree.ElementTree
https://docs.python.org/3.4/library/xml.etree.elementtree.html