Python, add nested elements to xml file

Question

I have an xml file like this:

<annotation>
    <folder>my-project-name</folder>
    <filename>red_noisy_snake_0000.png</filename>
    <object>
        <name>red_noisy_snake</name>
        <pose>Unspecified</pose>
        <truncated>Unspecified</truncated>
        <difficult>Unspecified</difficult>
        <bndbox>
            <xmin>618</xmin>
            <ymin>774</ymin>
            <xmax>1037</xmax>
            <ymax>858</ymax>
        </bndbox>
    </object>
</annotation>

And I need to add another 'object' field, similar to the one already present. I have the various values saved in variables (so, 'name', 'pose', 'truncated', the values in 'bndbox'...), and I just need to add it to the original xml file, so that at the end I should end up with something like:

<annotation>
    <folder>red_noisy_snake</folder>   --> CHANGED VALUE
    <filename>red_noisy_snake_0000.png</filename>
    <object>
        <name>red_noisy_snake</name>
        <pose>Unspecified</pose>
        <truncated>0</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>618</xmin>
            <ymin>774</ymin>
            <xmax>1037</xmax>
            <ymax>858</ymax>
        </bndbox>
    </object>
    <object>  --> ADDED OBJECT FIELD
        <name>child_seat</name>
        <pose>Unspecified</pose>
        <truncated>0</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>871</xmin>
            <ymin>25</ymin>
            <xmax>1190</xmax>
            <ymax>566</ymax>
        </bndbox>
    </object>
</annotation>

I know how to add a single, non nested element by using for example:

import xml.etree.ElementTree as ET

in_file = 'wrong.xml'

tree = ET.parse(in_file)
root = tree.getroot()

## add single field
add = ET.Element("tag_name")
add.tail = '\n\t'
add.text = 'content'
root.insert(5,add)
ET.dump(root)

but I can't figure out how to properly create the nested structure I need.

I would suggest you split your question into two (or more) questions; it's more likely you'll get responses that way. — Jack Fleeting
– Jack Fleeting, Commented Feb 17, 2021 at 17:43
Thanks, I figured part of the stuff in the original question, I removed it and left only the part I didn't solve yet! — Carlo
– Carlo, Commented Feb 17, 2021 at 19:53

Jack Fleeting · Accepted Answer · 2021-02-17 20:45:54Z

Fair warning: not everybody likes this approach - and prefer building elements manually - but when it comes to lengthy, nested node structures, I prefer using this template-like approach.

#this assumes all your new variables are located in one list; if not - you'll have to modify
inserts = ["child_seat","Unspecified", 0, 0, 871, 25, 1190, 566]

new_el = f"\n<object>\n        \
<name>{inserts[0]}</name>\n        <pose>{inserts[1]}</pose>\n <truncated>{inserts[2]}</truncated>\n      \
<difficult>{inserts[3]}</difficult>\n        <bndbox>\n            <xmin>{inserts[4]}</xmin>\n           \
<ymin>{inserts[5]}</ymin>\n            <xmax>{inserts[6]}</xmax>\n    \
<ymax>{inserts[7]}</ymax>\n        </bndbox>\n </object>\n"

add = ET.fromstring(new_el)
root.insert(3,add)
print(ET.tostring(root).decode())

The output should be what you're looking for.

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