Failing at inserting a new line in existing xml file

Question

I am currently writing a python code to manage an existing xml file.

I have this existing xml structure in a model file :

<MYPROJECT>
  <VERSION>2</VERSION>
  <LANGUAGE>english</LANGUAGE>
  <FILE>
    <FILENAME>Z</FILENAME>
  </FILE>
  <PANEL1>
    <SOURCE>
      <LAYER>MISSING</LAYER>
      <NAME>MISSING</NAME>
      <ID>MISSING</ID>
    </SOURCE>
  </PANEL1>
</MYPROJECT>

I need to be able to insert a new tag with its value in "Source" subelement. I want to get this in the end :

<MYPROJECT>
  <VERSION>2</VERSION>
  <LANGUAGE>english</LANGUAGE>
  <FILE>
    <FILENAME>toto</FILENAME>
  </FILE>
  <PANEL1>
    <SOURCE>
      <LAYER>A</LAYER>
      <NAME>B</NAME>
      <ID>C</ID>
      <NEW_TAG>XX</NEW_TAG>
    </SOURCE>
  </PANEL1>
</MYPROJECT>

To get this, I use xml.etree.ElementTree and the insert function. Here is my code :

import xml.etree.ElementTree as ET

cheminXML = r"mypath"

def majXML (cheminXML):
        tree = ET.parse(cheminXML)

        tagProject = ET.Element("MYPROJECT")
        tagPanel1 = ET.SubElement(tagProject,'PANEL1')
        tagSource = ET.SubElement(tagPanel1,'SOURCE')
        tagNewTag = ET.SubElement(tagSource, 'NEW_TAG')
        tagNewTag.text = "apple"
        print(tagNewTag.text)
        tagSource.insert(0,tagNewTag)

        tagFilename = tree.find(".//FILENAME")
        tagFilename.text = "toto"

        tree.write(cheminXML)

if __name__ == "__main__":
        majXML(cheminXML)

The new tag value is printed as it should. When I open my xml file, the filename value is "toto".

However, the new tag and its value are not written in the file.

Why is that ?

score 1 · Accepted Answer · answered Mar 22 '23 at 11:04

The following bit of your code is completely independent of the tree you loaded:

        tagProject = ET.Element("MYPROJECT")
        tagPanel1 = ET.SubElement(tagProject,'PANEL1')
        tagSource = ET.SubElement(tagPanel1,'SOURCE')
        tagNewTag = ET.SubElement(tagSource, 'NEW_TAG')
        tagNewTag.text = "apple"
        print(tagNewTag.text)
        tagSource.insert(0,tagNewTag)

Basically, you just create a new ET.Element from scratch, which you could write to a file with ET.ElementTree(tagProject).write('tagproject.xml').

On the other hand, you get tagFilename from the actual tree that you loaded, which means that you modify tree.

The solution is to make the other edits also by taking the nodes from tree rather than making new ones from scratch:

        tagSource = tree.find('.//SOURCE')   # tagSource is tree node, not a new one
        tagNewTag = ET.SubElement(tagSource, 'NEW_TAG')
        tagNewTag.text = "apple"

I understand. I tried calling my tag directly from tree as you said, and it works very well, thank you very much ! — theonewhodidnotknow, Mar 22 '23 at 12:55

Hermann12 · Answer 2 · 2023-03-22T16:58:56.517

As an alternative you can append the tag list, like:

import xml.etree.ElementTree as ET

tree = ET.parse("unknown.xml")
root = tree.getroot()

# redefine content
root.find(".//FILENAME").text = 'todo'
root.find(".//LAYER").text = 'A'
root.find(".//NAME").text = 'B'
root.find(".//ID").text = 'C'

# define and add a new element
new=ET.Element('NEW_TAG')
new.text = 'XX'
   
for elem in root.find('.//PANEL1'):
    elem.append(new)

ET.dump(root)
tree.write("New_unknown.xml", encoding='utf-8', xml_declaration=True)

Output file:

<?xml version='1.0' encoding='utf-8'?>
<MYPROJECT>
  <VERSION>2</VERSION>
  <LANGUAGE>english</LANGUAGE>
  <FILE>
    <FILENAME>todo</FILENAME>
  </FILE>
  <PANEL1>
    <SOURCE>
      <LAYER>A</LAYER>
      <NAME>B</NAME>
      <ID>C</ID>
      <NEW_TAG>XX</NEW_TAG>
    </SOURCE>
  </PANEL1>
</MYPROJECT>

Failing at inserting a new line in existing xml file

2 Answers2