Question

given this xml file, i would like to extract the data out from it. However, i have trouble extracting the data from <LandmarkPointListXml> onwards.

The XML file:

  <?xml version="1.0" encoding="utf-8"?>
  <Map xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <MapName>er</MapName>
  <MapURL>er.gif</MapURL>
  <Name>er</Name>
  <URL>er.gif</URL>
  <LandmarkPointListXml>
    <anyType xsi:type="LandmarkPointProperty">
      <LandmarkPointX>400</LandmarkPointX>
      <LandmarkPointY>292</LandmarkPointY>
      <LandmarkDesc>my room door</LandmarkDesc>
    </anyType>
    <anyType xsi:type="LandmarkPointProperty">
      <LandmarkPointX>399</LandmarkPointX>
      <LandmarkPointY>219</LandmarkPointY>
      <LandmarkDesc>bro room door</LandmarkDesc>
    </anyType>
  </LandmarkPointListXml>
  <RegionPointListXml />
</Map>

Python program:

    def GetMapData(self):
        result = ""
        haha = self.XMLdoc.firstChild #root node
        for child in haha.childNodes:
            if (cmp(child.nodeName,'LandmarkPointListXml')==0):
                result = result + '|' + self.loopLandmark(child.childNodes) + '|'
            else:
                result = result + child.firstChild.nodeValue + ','
        return result

    def loopLandmark(self, landmarks):
        result=""
        haha=landmarks.getElementsByTagName('anyType')
        for child in haha.childNodes:
            if (cmp(haha.firstChild.nodeName,'LandmarkPointX') == 0):
                result=result+child.firstChild.nodeValue+','
                ChildNode = ChildNode.nextSibling
                result=result+child.firstChild.nodeValue+','
                ChildNode = ChildNode.nextSibling
                result=result+child.firstChild.nodeValue
        return result

I was able to retrieve the result, “er,er.gif,er,er.gif,” till the program reaches <LandmarkPointListXml>.

Answer 1

This code is quite fragile. It makes strong assumptions on the XML input, and would fail if the XML was modified in a valid way (e.g. if is not immediately after ).

I suggest using a standard library when parsing XML, such as Element Tree ( http://docs.python.org/library/xml.etree.elementtree.html ) or lxml ( http://lxml.de ), which can also validate your XML input.

The code I’m writing below uses Element Tree and works on your XML input (I have removed the ‘self’ arguments to the parent class). It also tolerates (ignores) empty values in XML elements.

import xml.etree.ElementTree as ET

def GetMapData( xmlfile ):
    result = ""
    try:
        tree = ET.parse( xmlfile )
    except IOError, e:
        print "Failure Parsing %s: %s" % (xmlfile, e)
    root = tree.getroot() # root node
    for child in root:
        if ( child.tag == 'LandmarkPointListXml' ):
            result += '|' + loopLandmark(child) + '|'
        elif child.text is not None:
            result += child.text + ','
    return result

def loopLandmark( landmarks ):
    result=""
    for landmark in landmarks:
        if ( landmark.tag == 'anyType' ): # check also xsi:type="LandmarkPointProperty"?
            for child in landmark:
                if ( child.text and child.tag in [ 'LandmarkPointX', 'LandmarkPointY' ] ):
                    result += child.text + ','
    return result

GetMapData( 'xml.in' )