> A timedelta.toseconds method (or equivalent) makes no sense.
> The number of seconds in a day is not fixed (due to leap seconds) and
> relying on such a method would introduce subtle bugs.

You are misunderstanding what timedelta is. It is a fixed-length period
of time. It is stored as a number of (24x3600-second) days, seconds and
microseconds. There is no "start date" or "end date", so the concept of
leap seconds just does not apply.