Can't convert expression to float

I'm trying to learn the ins and outs of symbolic manipulation in python (I'm a beginner).

I have the following basic code, and the output is giving me an error telling me that it "can't convert expression to float".

What's wrong with this code:

from sympy import *
from math import *

def h(x):
    return log(0.75392 * x)

x = symbols('x')
hprime = h(x).diff(x)

print(hprime)