Python3's '/' operator is different from Python2's '/' operator. This is clear when you try to overload them. Python2's is called '__div__', while Python3's is '__truediv__'.
The Python3's operator '/' (on numbers) is defined to return a float, and it'll convert any integer parameters as required. The same is true for other operators, like 'True + True' being 2.
Because of these definitions, you should consider the operators as explicit conversions. 'total / sum' is less explicit than 'total / float(sum)', but still clear enough.
And about guidelines, there are others that fit this case:
Simple is better than complex.
Flat is better than nested.
Readability counts.
[...] practicality beats purity.
PS: I think you made an important argument and I'm glad you did it, even though I disagree with it. I fail to see why you are getting downvotes.
I went to check out the operation and it seems a on two ints returns an int if the power is a nonnegative int, and a float if it's negative nonzero, in both 2.7 and 3. I didn't expect this kind of inconsistency from python, really.
I guess it does follow the last line of the guidelines there, though. Looking at this power example, the division returning float now is actually an increase in consistency.
I think it's better to think of it as division being an operation that returns the appropriate type for the operation, i.e., a float where necessary. The type of the operands remain unchanged so "upcasting" is not applicable if you ask me.
