>Python definitely returns NaNs when required to by the spec (which is to say: whenever maths is happening with NaNs). I think you're getting confused between p

>Python definitely returns NaNs when required to by the spec (which is to say: whenever maths is happening with NaNs). I think you're getting confused between propagation and coercion. It returns NaNs in absurdly unused mathematical operations like: x=float('nan') x = float("inf") * 0 Javascript returns it on any math operation on an 'undefined' which is another bad value likely to occur in JS. It basically never happens in practice for python. Yes python will propogate a NaN but the operations that instantiate a NaN are so absurd and rare that effectively NaNs aren't used or ever encountered in python. I personally use floating point infinite to create initializer values that are always greater then everything else for algos involving min, but effectively I've basically never seen infinite used in code either. There is a hole here in that one day I may encounter the NaN because as shown above... usage of infinite is one of the ways to generate a NaN, but again this is so rare that effectively it never happens. I am not confused. I believe you're just getting a bit pedantic.