inserting newlines in xml file generated via xml.etree.ElementTree in python

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UPDATE 2022 – python 3.9 and later versions

For python 3.9 and later versions the standard library includes xml.etree.ElementTree.indent:

Example:

import xml.etree.ElementTree as ET

root = ET.fromstring("<fruits><fruit>banana</fruit><fruit>apple</fruit></fruits>""")
tree = ET.ElementTree(root)
    
ET.indent(tree, '  ')
# writing xml
tree.write("example.xml", encoding="utf-8", xml_declaration=True)

Thanks Michał Krzywański for this update!

BEFORE python 3.9

I found a new way to avoid new libraries and reparsing the xml.
You just need to pass your root element to this function (see below explanation):

def indent(elem, level=0):
    i = "\n" + level*"  "
    if len(elem):
        if not elem.text or not elem.text.strip():
            elem.text = i + "  "
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
        for elem in elem:
            indent(elem, level+1)
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
    else:
        if level and (not elem.tail or not elem.tail.strip()):
            elem.tail = i

There is an attribute named “tail” on xml.etree.ElementTree.Element instances.
This attribute can set an string after a node:

"<a>text</a>tail"

I found a link from 2004 telling about an Element Library Functions that uses this “tail” to indent an element.

Example:

root = ET.fromstring("<fruits><fruit>banana</fruit><fruit>apple</fruit></fruits>""")
tree = ET.ElementTree(root)
    
indent(root)
# writing xml
tree.write("example.xml", encoding="utf-8", xml_declaration=True)

Result on “example.xml”:

<?xml version='1.0' encoding='utf-8'?>
<fruits>
    <fruit>banana</fruit>
    <fruit>apple</fruit>
</fruits>

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