Very good. I also find the division rounding and symmetry in your implementation aesthetically appealing. I think I just instinctively reach for half-open inter

Very good. I also find the division rounding and symmetry in your implementation aesthetically appealing. I think I just instinctively reach for half-open intervals for reasons unrelated to this particular problem. For signed search ranges, if you modify my implementation above to compute the midpoint as (lo + hi) // 2 and (lo + hi) < 0 and the language rounds integer division toward zero, you gain a rounding-related bug. In this sort of circumstance, your approach does not gain that bug because it doesn't care which way division is rounded. Python doesn't have overflow and rounds down, so ~all of the errors we can make on that line won't happen anyway :) If the range is unsigned, lo-1 is likely to be MAX_VALUE, but it seems like it still does the right thing.