Python etree control empty tag format

Question

When creating an XML file with Python's etree, if we write to the file an empty tag using SubElement, I get:

<MyTag />

Unfortunately, our XML parser library used in Fortran doesn't handle this even though it's a correct tag. It needs to see:

<MyTag></MyTag>

Is there a way to change the formatting rules or something in etree to make this work?

Answer 1

As of Python 3.4, you can use the short_empty_elements argument for both the tostring() function and the ElementTRee.write() method:

>>> from xml.etree import ElementTree as ET
>>> ET.tostring(ET.fromstring('<mytag/>'), short_empty_elements=False)
b'<mytag></mytag>'

In older Python versions, (2.7 through to 3.3), as a work-around you can use the html method to write out the document:

>>> from xml.etree import ElementTree as ET
>>> ET.tostring(ET.fromstring('<mytag/>'), method='html')
'<mytag></mytag>'

Both the ElementTree.write() method and the tostring() function support the method keyword argument.

On even earlier versions of Python (2.6 and before) you can install the external ElementTree library; version 1.3 supports that keyword.

Yes, it sounds a little weird, but the html output mostly outputs empty elements as a start and end tag. Some elements still end up as empty tag elements; specifically <link/>, <input/>, <br/> and such. Still, it's that or upgrade your Fortran XML parser to actually parse standards-compliant XML!

Answer 2

This was directly solved in Python 3.4. From then, the write method of xml.etree.ElementTree.ElementTree has the short_empty_elements parameter which:

controls the formatting of elements that contain no content. If True (the default), they are emitted as a single self-closed tag, otherwise they are emitted as a pair of start/end tags.

More details in the xml.etree documentation.