> Does that support the other way -- or do we never lose a leap second anyway?
> (showing ignorance here)
Alexander covered the Python part of this, ...
No, I did not. I did not realize that the question was about skipping a second instead of inserting it. Yes, regardless of whether it is possible given the physics of Earth rotation, negative leap seconds can be supported. They simply become "gaps" in PEP 495 terminology. Check out PEP 495 and read "second" whenever you see "hour". :-)