William Purcell wrote: > I am writing a application to calculate pressure drop for a piping > network. Namely a building sprinkler system. This will be a > command line program at first with the system described in xml (at > least that is how I think I want to do it). > > An important part of this calculation is finding the 'hydraulically > most remote' sprinkler. This is something that I could specify with > an attribute for now and later think about how to automate it. I > need to walk through the dom tree until I find a node of type > "sprinkler" that has an attribute of hydraulically_most_remote with > a value of True. > > After I find this I need to break the itterator/for loop and then > start walking backwards keeping a running total of the pressure drop > until I reach a node that has multiple pipesections and then walk to > the end of each branch and calculate the pressure drop, and then add > them to the branch that contained the hydraulically most remote > sprinkler, and then move on, repeating this until I walk all the way > back to the inflow node. > > I am having trouble finding a decent python/xml resource on the web. > I have ordered Python & XML by Jones and Drake, but I am anxious to > get something started. The only decent online resource that I can > seem to find is > > http://pyxml.sourceforge.net/topics/howto/xml-howto.html > > which doesn't seem to be a very comprehensive how-to. > > Do demonstrate just about everything I know about xml and python I > attached t.py and ex.xml. > > Another thing that is confusing is dir(walker) does not show walker > having an attribute currentNode and dir(walker.currentNode) does not > show walker.currentNode having an attribute tagName.
Use lxml2 and xpath. http://codespeak.net/lxml/ http://codespeak.net/lxml/xpathxslt.html See the below piece of code to get you started: import lxml.etree as et xml = """<?xml version="1.0"?> <project name="test"> <inflow static="60" residual="20"> <pipesection diameter="1.05" length="10"> <node id="H1" k="5.6" type="sprinkler"> <pipesection diameter="1.05" length="4"> <node id="1" type="T"> <pipesection diameter="1.05" length="6"> <node id="H2" hydraulically_most_remote="True"> </node> </pipesection> <pipesection diameter="1.05" length="5"> <node id="H3"> </node> </pipesection> </node> </pipesection> </node> </pipesection> </inflow> </project>""" project = et.fromstring(xml) hydraulically_most_remote = project.xpath("//no...@hydraulically_most_remote='True']")[0] print hydraulically_most_remote.attrib["id"] # find node with multiple pipesections that's upwards def find_mp_node(node): pipesections = node.xpath("pipesection") if len(pipesections) > 1: return node parent = node.getparent() if parent is not None: return find_mp_node(parent) print find_mp_node(hydraulically_most_remote).attrib["id"] -- http://mail.python.org/mailman/listinfo/python-list
