Python how to keep the XML comment exist after write a new value using Python?

Question

I have an XML file then need to update some value. My XML file contains the comment. I would like to keep the comment after writing the XML, but it disappeared.

Here is my XML:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Data System -->
<process>
     <!-- Student Name -->
     <NAME source="hsfg" class="hshah" property="Name">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </NAME>
     <!-- Exercise Number -->
     <number source="hsfg" class="hgdgf" property="gagfa">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </number>
     <!-- Exam ID -->
     <id source="hsfg" class="gfdg" property="fadg">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </id>
</process>

This is the value that I need to update

<!-- Student Name -->
     <NAME source="hsfg" class="hshah" property="Name">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </NAME>

become this:

<!-- Student Name -->
     <NAME source="hsfg" class="hshah" property="Name">
          <VALUE type="string">new value</VALUE>
          <VALUE type="None"></VALUE>
     </NAME>

My code:

read = ET.parse('test.xml').getroot()
parent = read.find('.//NAME[@property="Name"]')
change = parent.find('VALUE[@type="string"]')
change.text = 'new value'
tree = ET.ElementTree(read)
tree.write("test.xml")

The output of the test.xml file become this. the comment and <?xml version="1.0" encoding="UTF-8"?> dissapeared.

<process>
     
     <NAME source="hsfg" class="hshah" property="Name">
          <VALUE type="string">new value</VALUE>
          <VALUE type="None" />
     </NAME>
     
     <number source="hsfg" class="hgdgf" property="gagfa">
          <VALUE type="string" />
          <VALUE type="None" />
     </number>
     
     <id source="hsfg" class="gfdg" property="fadg">
          <VALUE type="string" />
          <VALUE type="None" />
     </id>
</process>

BUT my expectation output, the structure and the comment still the same as before update the value like this:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Data System -->
<process>
     <!-- Student Name -->
     <NAME source="hsfg" class="hshah" property="Name">
          <VALUE type="string">new value</VALUE>
          <VALUE type="None"></VALUE>
     </NAME>
     <!-- Exercise Number -->
     <number source="hsfg" class="hgdgf" property="gagfa">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </number>
     <!-- Exam ID -->
     <id source="hsfg" class="gfdg" property="fadg">
          <VALUE type="string"></VALUE>
          <VALUE type="None"></VALUE>
     </id>
</process>

Abhi_J · Accepted Answer · 2021-03-17 06:42:23Z

Use ET.XMLParser to preserve comments
Use encoding and xml_declaration arguments in write() function to write xml declaration Try the following code:

import xml.etree.ElementTree as ET
parser = ET.XMLParser(target=ET.TreeBuilder(insert_comments=True))

read = ET.parse('newXml.xml', parser=parser).getroot()
parent = read.find('.//NAME[@property="Name"]')
change = parent.find('VALUE[@type="string"]')
change.text = 'new value'
tree = ET.ElementTree(read)
tree.write("test.xml", encoding='utf-8', xml_declaration=True)

you can also avoid variable read and just use tree:

import xml.etree.ElementTree as ET
parser = ET.XMLParser(target=ET.TreeBuilder(insert_comments=True))

tree = ET.parse('newXml.xml', parser=parser)
parent = tree.find('.//NAME[@property="Name"]')
change = parent.find('VALUE[@type="string"]')
change.text = 'new value'
tree.write("test.xml", encoding='utf-8', xml_declaration=True)

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