Traversing from one node in xml to another using Python

Question

I am very new to XML with Python and I have the following XML string that I get as a response from a network device:

'<Response MajorVersion="1" MinorVersion="0"><Get><Configuration><OSPF MajorVersion="19" MinorVersion="2"><ProcessTable><Process><Naming><ProcessName>1</ProcessName></Naming><DefaultVRF><AreaTable><Area><Naming><AreaID>0</AreaID></Naming><Running>true</Running><NameScopeTable><NameScope><Naming><InterfaceName>Loopback0</InterfaceName></Naming><Running>true</Running><Cost>1000</Cost></NameScope><NameScope><Naming><InterfaceName>Loopback1</InterfaceName></Naming><Running>true</Running><Cost>1</Cost></NameScope><NameScope><Naming><InterfaceName>GigabitEthernet0/0/0/0</InterfaceName></Naming><Running>true</Running><Cost>1</Cost></NameScope></NameScopeTable></Area></AreaTable></DefaultVRF><Start>true</Start></Process></ProcessTable></OSPF></Configuration></Get><ResultSummary ErrorCount="0" /></Response>'

I have the following code to retrieve the interface information along with the interface cost associated with it. However I would also like to get the 'AreaID' tag associated with each interface as part of my dictionary. Unable to navigate the tree correctly to retrieve the AreaID tag value:

for node in x.iter('NameScope'):
int_name = str(node.find('Naming/InterfaceName').text)
d[int_name] = {}
d[int_name]['cost'] = str(node.find('Cost').text)

This code gives the following output when 'd' is printed:

{'GigabitEthernet0/0/0/0': {'cost': '1'},
 'Loopback0': {'cost': '1000'},
 'Loopback1': {'cost': '1'}}

I want something like this in the output:

{'GigabitEthernet0/0/0/0': {'cost': '1', 'area': 0},
 'Loopback0': {'cost': '1000', 'area': 0},
 'Loopback1': {'cost': '1', 'area': 0}}

Any suggestions or modifications to my code will be really appreciated!

alecxe · Accepted Answer · 2016-04-14 20:02:38Z

1

I would use the preceding notation:

node.xpath(".//preceding::AreaID")[0].text

Complete code I am executing:

from lxml import etree as ET

x = ET.parse("input.xml")
d = {}
for node in x.iter('NameScope'):
    int_name = str(node.find('Naming/InterfaceName').text)
    d[int_name] = {
        'cost': str(node.find('Cost').text),
        'area': node.xpath(".//preceding::AreaID")[0].text 
    }

print(d)

Prints:

{
    'Loopback0': {'cost': '1000', 'area': '0'}, 
    'Loopback1': {'cost': '1', 'area': '0'}, 
    'GigabitEthernet0/0/0/0': {'cost': '1', 'area': '0'}
}

edited Apr 14, 2016 at 20:02

answered Apr 14, 2016 at 19:57

alecxe

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4 Comments

pypep278 Over a year ago

Thanks for your reply. However, 'x' is an xml.etree.ElementTree.Element object. Hence, node doesnt have the xpath attribute. I am on Python 2.7. Also, I tried what you suggested by doing this: "area = str(node.find(".//preceding::AreaID")[0].text)" and I got this error "SyntaxError: prefix 'preceding' not found in prefix map "

pypep278 Over a year ago

Also, my input is not an xml file, but an xml.etree.ElementTree.Element object.

alecxe Over a year ago

@pypep278 well, it works for me even if I define a data string variable and define x as x = ET.fromstring(data). What happens if you use xpath() method?

pypep278 Over a year ago

Thank you so much! I was using the following import as opposed to yours and hence it failed for me: import xml.etree.ElementTree as ET

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