f= lambda x: -0.1*x**4-0.15*x**3-0.5*x**2-0.25*x+1.2

x=0.5
h=0.25

Dh1=(f(x+2*h)-f(x-2*h))/((x+2*h)-(x-2*h))
Dh2=(f(x+h)-f(x-h))/((x+h)-(x-h))

D=(4*Dh2-Dh1)/3

print('Dh1= %f Dh2= %f D= %f'%(Dh1,Dh2,D))