jessenoller.com

XPath for ElementTree (ElementFilter)

So, in my great big XML library, I wanted to build a query-like interface for the QA Automaters to be able to use that would abstract out a lot of the grunt work of getting the XML object, setting up the Elementtree object and doing the basic parsing we need.

What I settled on was a 3 Module approach:

GetXML: grabs the XML from the IP/URL, returns an ElementTree.fromstring() object
BasicParse: Extends GetXML, does the basic parsing and some looping of the GetXML calls for the XML

The key was the third module I wanted to build: QueryInterface - I wanted to use XPath syntax to be able to do targetted searches within the XML tree and allow users to call a series of pre-built queries (with the ability to pass in custom queries).

ElementTree has very rudimentary XPath support - the real savior in this project was an ElementTree addon called ElementFilter. ElementFilter is a wrapper that allows you to "Find or remove nodes from ElementTree XML using an XPath-like filter."

It's a perfect fit. All of the methods in the QueryInterface class are super simple:

def getNodeStatus(self):
"""
Returns a list of objects of all node/status inside the tree
"""
path = r"node/status[@stateString=='AVAIL']/"
return findall(self.tree, path)

It really made life easier for me. For custom queries I can allow people to pass through the r"%s" % (query) section:

def customQuery(self, query):
"""
Expects: an xpath-like query in format
Returns: A list of objects containing all results for the query.
"""
path = r"%s" % (query)
return findall(self.tree, path)

Viola! If I were you, go check out ElementFilter