We have to cut of the first line and the first column:
>>> sales[1:, 1:].astype(np.float)
array([[ 1245.89, 2220. , 1936.25],
[ 1289.99, 2405.14, 2064.32],
[ 1379.04, 1984.9 , 1879.3 ],
[ 1450.89, 2178.34, 2027.51],
[ 1680.98, 2163.86, 2147.96],
[ 1860.33, 2079.97, 2201.28],
[ 2103.54, 2310.92, 2466.17],
[ 2354.54, 2360.46, 2634.07],
[ 2648.1 , 2433.92, 2839.12],
[ 2971.56, 2566.19, 3093.72],
[ 3338.08, 2661.59, 3351.77],
[ 3747.93, 2774.12, 3643.6 ],
[ 4209.09, 2901.24, 3972.25],
[ 4726.47, 3026.45, 4331.24],
[ 5307.72, 3162.8 , 4732.13]])