I agree -- it's not at all intuitive that the floor division returns a decimal number of seconds, while float division raises an error.  This should probably be cleaned up.   

In python 3.4, both float division and integer division return decimal numbers of seconds -- that's not all that intuitive, either.  

Python 3.4.0a0 (default:d5536c06a082+, Jul 11 2013, 20:23:54) 
[GCC 4.8.1] on linux
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>>> from datetime import timedelta
>>> print(timedelta(seconds=3)/2)
0:00:01.500000
>>> print(timedelta(seconds=3)//2)
0:00:01.500000