lxml and xpath(?)

[Doug OLeary]

Hey;

Reasonably new to python and incredibly new to xml much less trying to parse it. I need to identify cluster nodes from a series of weblogic xml configuration files. I've figured out how to get 75% of them; now, I'm going after the edge case and I'm unsure how to proceed.

Weblogic xml config files start with namespace definitions then a number of child elements some of which have children of their own.

The element that I'm interested in is <server> which will usually have a subelement called <listen-address> containing the hostname that I'm looking for.

Following the paradigm of "we love standards, we got lots of them", this model doesn't work everywhere. Where it doesn't work, I need to look for a subelement of <server> called <machine>. That element contains an alias which is expanded in a different root child, at the same level as <server>.

So, picture worth a 1000 words:

<?xml version='1.0' encoding='UTF-8'?>
< [[ heinous namespace xml snipped ]] >
   <name>[[text]]</name>
   ...
   <server>
      <name>EDIServices_MS1</name>
      ...
      <machine>EDIServices_MC1</machine>
      ...
   </server>
   <server>
      <name>EDIServices_MS2</name>
      ...
      <machine>EDIServices_MC2</machine>
      ...
   </server>
   <machine xsi:type="unix-machineType">
     <name>EDIServices_MC1</name>
     <node-manager>
       <name>EDIServices_MC1</name>
       <nm-type>SSL</nm-type>
       <listen-address>host001</listen-address>
       <listen-port>7001</listen-port>
     </node-manager>
   </machine>
   <machine xsi:type="unix-machineType">
     <name>EDIServices_MC2</name>
     <node-manager>
       <name>EDIServices_MC2</name>
       <listen-address>host002</listen-address>
       <listen-port>7001</listen-port>
     </node-manager>
   </machine>
</domain>

So, running it on 'normal' config, I get:

$ ./lxml configs/EntsvcSoa_Domain_config.xml  
EntsvcSoa_CS    => host003.myco.com
EntsvcSoa_CS   => host004.myco.com

Running it against the abi-normal config, I'm currently getting:

$ ./lxml configs/EDIServices_Domain_config.xml
EDIServices_CS => EDIServices_MC1
EDIServices_CS => EDIServices_MC2

Using the examples above, I would like to translate EDIServices_MC1 and EDIServices_MC2 to host001 and host002 respectively.

The primary loop is:

for server in root.findall('ns:server', namespaces):
  cs = server.find('ns:cluster', namespaces)
  if cs is None:
    continue
  # cluster_name = server.find('ns:cluster', namespaces).text
  cluster_name = cs.text
  listen_address = server.find('ns:listen-address', namespaces)
  server_name = listen_address.text
  if server_name is None:
    machine = server.find('ns:machine', namespaces)
    if machine is None:
      continue
    else:
      server_name = machine.text

  print("%-15s => %s" % (cluster_name, server_name))

(it's taken me days to write 12 lines of code... good thing I don't do this for a living :) )

Rephrased, I need to find the <listen-address> under the <machine> child who's name matches the name under the corresponding <server> child. From some of the examples on the web, I believe xpath might help but I've not been able to get even the simple examples working. Go figure, I just figured out what a namespace is...

Any hints/tips/suggestions greatly appreciated especially with complete noob tutorials for xpath.

Thanks for your time.

Doug O'Leary