XPath is used to navigate through elements and attributes in an XML document. XPath is a major element in W3C's XSLT standard - and XQuery and XPointer are both built on XPath expressions.
PyFacebook is currently best-tested with Django, and if you are just starting out with Python web development, the author highly recommends this combination :-). If you'd rather use another framework, there are also Pylons and other WSGI helpers in PyFacebook as well.