[Christian]
> float(td1) / float(td2) which is far more obvious than td1 / td2

To me, td1/td2 is more obvious that float(td1)/float(td2).

float(td) involves an arbitrary choice, to return time in *seconds* 
(rather than days, or milliseconds, or ...);  I think this violates 
EIBTI.  To me, the obvious and easy-to-read way to get the number
of seconds is to do the division:

seconds_in_td = td1 / timedelta(seconds = 1)