Write data in xml based on attribute key

Question

I have an xml file as below and I want to read data from my device and write the data into "value" column on certain name by using python script.

<TopoDefs>   
<Device Name="SNB" LogicalType="CORE" IdCode="0x03886A21" Mask="0xf0000000">
<Variable name="A0" value="0x52001321" type="GREEN" />
<Variable name="A1" value="0x51001321" type="GREEN" />
<Variable name="A2" value="0x03001321" type="GREEN" />
<Variable name="A3" value="0x14001321" type="GREEN" />
<Variable name="B0" value="0x5A001321" type="BLUE" />
<Variable name="B1" value="0x51001321" type="BLUE" />
<Variable name="B2" value="0x04001321" type="BLUE" />
<Variable name="B3" value="0x05001321" type="BLUE" />
</Device>
</TopoDefs>

May I asks how to I point to the variable A0 to write a new data on "value" attribute? What is the differences among find, findall, iterfind, itertext?

root · Accepted Answer · 2012-10-17 17:25:19Z

1

Using lxml , that I argue is the best tool available for the task:

from lxml import etree as ET


>>> root = ET.fromstring('<TopoDefs><Device Name="SNB" LogicalType="CORE" IdCode="0x03886A21" Mask="0xf0000000"><Variable name="A0" value="0x52001321" type="GREEN" /><Variable name="A1" value="0x51001321" type="GREEN" /><Variable name="A2" value="0x03001321" type="GREEN" /><Variable name="A3" value="0x14001321" type="GREEN" /><Variable name="B0" value="0x5A001321" type="BLUE" /><Variable name="B1" value="0x51001321" type="BLUE" /><Variable name="B2" value="0x04001321" type="BLUE" /><Variable name="B3" value="0x05001321" type="BLUE" /></Device></TopoDefs>')
>>> root.xpath('.//Variable[@name="A0"]')[0].attrib['value']='test'
>>> print ET.tostring(root,pretty_print=True)
<TopoDefs>
  <Device Name="SNB" LogicalType="CORE" IdCode="0x03886A21" Mask="0xf0000000">
    <Variable name="A0" value="test" type="GREEN"/>
    <Variable name="A1" value="0x51001321" type="GREEN"/>
    <Variable name="A2" value="0x03001321" type="GREEN"/>
    <Variable name="A3" value="0x14001321" type="GREEN"/>
    <Variable name="B0" value="0x5A001321" type="BLUE"/>
    <Variable name="B1" value="0x51001321" type="BLUE"/>
    <Variable name="B2" value="0x04001321" type="BLUE"/>
    <Variable name="B3" value="0x05001321" type="BLUE"/>
  </Device>
</TopoDefs>

Or you can loop through Variables and change all values as I understood you wanted:

>>> for i in root.xpath('.//Variable'):
...     i.attrib['value']='CHANGE'
...     
>>> print ET.tostring(root,pretty_print=True)
<TopoDefs>
  <Device Name="SNB" LogicalType="CORE" IdCode="0x03886A21" Mask="0xf0000000">
    <Variable name="A0" value="CHANGE" type="GREEN"/>
    <Variable name="A1" value="CHANGE" type="GREEN"/>
    <Variable name="A2" value="CHANGE" type="GREEN"/>
    <Variable name="A3" value="CHANGE" type="GREEN"/>
    <Variable name="B0" value="CHANGE" type="BLUE"/>
    <Variable name="B1" value="CHANGE" type="BLUE"/>
    <Variable name="B2" value="CHANGE" type="BLUE"/>
    <Variable name="B3" value="CHANGE" type="BLUE"/>
  </Device>
</TopoDefs>

edited Oct 17, 2012 at 17:25

answered Oct 17, 2012 at 17:02

root

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2 Comments

yamcake01096 Over a year ago

sorry im new in python, may I know how to I install lxml library in Windows?

root Over a year ago

lxml.de/installation.html , this should guide you through the process. there are binary packages available for windows, i suggest you choose one of them.

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