This is a bit of Python trivia but Python containers can store items that are self references.

The way this works is that in Python a list just stores references to Python objects so you can just have a reference to the container. You can create such a list like this:

>>> foo = ['bar', 'baz']
>>> foo.append(foo)
>>> foo
['bar', 'baz', [...]]
>>> foo[2] is foo

So you can see here from the object identity test that foo has a self reference in it now.

This knowledge can be useful sometimes (like explaining to people why there's 2 garbage collection mechanisms in CPython) but for the most part this will just be a bit of trivia.