Sorry, Mark - I took a true thing and careleslly turned it into a false thing ;-)

It's math.floor(a_float) that returns an int in Py3, not floor division of floats.  So, yup, no real problem with returning -0.0 after all; it's just that it can't be _explained_ via

   x // y means math.floor(x / y)

is Py3 for float x and y, since the latter returns an int bur the former a float.

But looks like it can be "explained" via

   x // y means divmod(x, y)[0]