Plotting error message regarding numerical type of function arguments

I am trying to plot the following function: x = var('x') def y(x): return RR(len(prime_range(floor(0.95 * x), floor(1.25 * x))) / round(1.25 * x - 0.95 * x)) I am not sure whether it is well-constructed mathematically, but it's trying to check the density of prime numbers around a given value `x` I am using the `floor()` function because I'm not sure that `prime_range()` accepts non-integers. If I test the function with random real values of `x` I get a plausible output without errors. However, when I try to plot the function as in: plot(y(x), (x, 5, 20)) I get the following error message: TypeError: unable to convert floor(0.950000000000000*x) to an integer and argument is also not real: unable to simplify to float approximation I don't understand why this input cannot be understood as real by sagemath, or why the floor is not an integer.