What does it yield?
Are you using ArcMap? (your print statement suggests python 2.7)
Do you have any null areas/values?
Of course you could use RasterToNumPyArray and use numpy to do the work quickly.
import numpy as np
a = np.arange(0, 12.).reshape(4, 3)
a
array([[ 0., 1., 2.],
[ 3., 4., 5.],
[ 6., 7., 8.],
[ 9., 10., 11.]])
a_min = np.nanmin(a)
a_max = np.nanmax(a)
a_stand = (a - a_min) / (a_max - a_min)
a_stand
array([[0. , 0.09090909, 0.18181818],
[0.27272727, 0.36363636, 0.45454545],
[0.54545455, 0.63636364, 0.72727273],
[0.81818182, 0.90909091, 1. ]])
... sort of retired...