How to add comments in XML using python

Question

XML i am parsing:

<List>
    <Item>
        <Price>
            <Amount>100</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>

In Output XML i want to add a comment above Next_Item:

<List>
    <Item>
        <Price>
            <Amount>100</Amount>
            <!--Not-Needed-->
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>

I tried following:

doc = etree.parse('XML1')
for id in doc.xpath('//Item/Price/Next_Item/text()'):
id = etree.Comment('Not-Needed')
root = doc.getroot()
 root.insert(1, comment)

Its adding comment at the top of file instead of above 'next_item' element.

As here

root.insert(1, comment) [1 is index]

so is there a way where instead of index number i can pass a variable so i can add comment to number of places . for example whenever it finds 'next_item' it has to add a comment

output i am getting is:

<List>
<!--Not-Needed--><!--Not-Needed--><!--Not-Needed--><!--Not-Needed--><!--Not-Needed--><!--Not-Needed--><!--Not-Needed--><!--Not-Needed-->
    <Item>
        <Price>
            <Amount>100</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>

Grateful for your help.

I don't see that XPath //Item/Price/Next_Item() working at all, what are the () at the end good for? Have you considered using XSLT to insert the comment nodes? — Martin Honnen
– Martin Honnen, Commented Oct 20, 2022 at 8:04
@MartinHonnen I have changed the path to //Item/Price/Next_Item/text() I have never worked in XSLT yet — Anonymous
– Anonymous, Commented Oct 20, 2022 at 8:12
Your input sample has four Next_Item elements and your text seems to suggest you want to add a comment before each of them, yet your output sample only shows one comment before the first Next_Item element. Please clarify. — Martin Honnen
– Martin Honnen, Commented Oct 20, 2022 at 8:31
@MartinHonnen I have edited my question with XML i am getting and XML I am looking for root.insert(1, comment) only takes index but I want to pass a variable which will search the Item/Price/Id if its 100 then it will add comment above Next_Item — Anonymous
– Anonymous, Commented Oct 20, 2022 at 11:11

balderman · Accepted Answer · 2022-10-20 12:56:21Z

Try the below (Note that no external lib is required)

import xml.etree.ElementTree as ET

xml = '''<List>
    <Item>
        <Price>
            <Amount>100</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>'''
root = ET.fromstring(xml)
first_price = root.find('.//Item/Price')
first_price.insert(1, ET.Comment('Not-Needed'))
ET.dump(root)

output

<List>
    <Item>
        <Price>
            <Amount>100</Amount>
            <!--Not-Needed-->
             <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>

Martin Honnen · Accepted Answer · 2022-10-20 12:50:42Z

I think this is a good use case for an XSLT transformation and lxml supports XSLT 1.0:

<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="1.0">
  
  <xsl:output indent="yes"/>

  <xsl:template match="@* | node()" name="identity">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="Item/Price[Amount = 100]/Next_Item[1]">
    <xsl:comment>Not-needed</xsl:comment>
    <xsl:call-template name="identity"/>
  </xsl:template>

</xsl:stylesheet>

So a small Python sample using lxml to run the above XSLT against the shown sample input and write the transformation result to the file result1.xml is e.g.

from lxml import etree as ET

def xslt_usage_example():
    xml = ET.XML("""<List>
    <Item>
        <Price>
            <Amount>100</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
         <Price>
            <Amount>200</Amount>
            <Next_Item>
                <Name>Apple</Name>
            </Next_Item>
            <Next_Item>
                <Name>Orange</Name>
            </Next_Item>
        </Price>
    </Item>
</List>""")

    transformer = ET.XSLT(ET.XML("""<xsl:stylesheet
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="1.0">
    
  <xsl:output method="xml" indent="yes" encoding="UTF-8"/>

  <xsl:template match="@* | node()" name="identity">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="Item/Price[Amount = 100]/Next_Item[1]">
    <xsl:comment>Not-needed</xsl:comment>
    <xsl:call-template name="identity"/>
  </xsl:template>

</xsl:stylesheet>"""))

    result = transformer(xml)

    result.write_output("result1.xml")

if __name__ == '__main__':
    xslt_usage_example()

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