Why does 0.1 and 0.2 = 0.30000000000000004?
I've said this before, but I wish python and other high level languages defaulted to decimal for the literals, and made float something you had to do explicitly.  My reasoning behind this is that floating point math is almost always an implementation detail, instead of what you're actually trying to do.   Sure, decimal would be slower, but forcing people to use float as an optimization would remind them to mitigate the risks with rounding or whatever.