now we really have gotten OT...

But thanks! that was my question!


Alexander covered the Python part of this, so I'll answer the possible
higher-level question:  we haven't yet needed a "negative" leap
second, and it's considered unlikely (but not impossible) that we ever
will.  That's because the Earth's rotation is inexorably slowing ,so
the mean solar day inexorably lengthens when measured by SI seconds.

Other things can cause the Earth's rotation to speed up temporarily
(like some major geological events), but they've only been able to
overcome factors acting to slow rotation for brief periods, and never
yet got near to overcoming them by a full second.


Christopher Barker, Ph.D.

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