The preview of the new Python 3 port has broken HTML escaping in the XML feeds

I am using:
O.S: Fedora 40
Browser: Firefox 131.0.2
Platform: desktop

Problem

The preview of the new Python 3 port has broken HTML escaping in the XML feeds

eg try to view this in the browser:

https://planetpython.org/3/rss10.xml

and it will complain about undefined entities, due to having raw unescaped HTML in the XML document

By comparison the original Python 2 code escaped HTML in the feed

$ wget https://planetpython.org/rss10.xml
$ grep "content:encoded" rss10.xml | head -1
	<content:encoded>&lt;p&gt;As is probably apparent from the sequence of blog posts about the topic in the
$ wget https://planetpython.org/3/rss10.xml
$ grep "content:encoded" rss10.xml.1 | head -1
	<content:encoded><p>As is probably apparent from the sequence of blog posts about the topic in the

Details

This problem is caused by a mistake in the python 3 conversion done in #577, specially in commit https://github.com/python/planet/pull/577/commits/86e31f90403c4659471396beeba922584e08d12e replaced code patterns like:

feed[key] = sanitize.HTML(feed[key])

with

feed[key] = Markup(feed[key])

which is not providing functionally equivalent behaviour.

The sanitize.HTML method would parse the HTML and strip out various undesirable elements and attributes, and escaping was later performed by the template processor.

The Markup method will not parse anything, it'll just wrap the str in a Markup class, as a way to designate it as being safe to use as-is without further escaping. As a result when you later try to escape the variable in jinga using ... | e, it will do nothing at all, resulting in raw HTML being put into the XML document, leading to the later parsing errors.

I think either the original sanitizer code needs to be re-instated and made to work with py3, or perhaps an external library such as https://github.com/matthiask/html-sanitizer/ could be leveraged ?

Start by inspecting the Python 3 feed generation affected by commit 86e31f90403c4659471396beeba922584e08d12e in #577, comparing the former sanitize.HTML call with Markup. Verify the fix against https://planetpython.org/3/rss10.xml and confirm content:encoded HTML is escaped so the XML parses without undefined-entity errors.