Strange sum

strange_sum.py

>>> l = [4873.40374783,
         5821.07686377,
         5781.99852348,
         5555.53769711,
         0.0,
         0.0,
         0.0,
         0.0]
>>> a = np.array(l)
>>> b = np.empty((8, 2))
>>> b[:] = a[:, np.newaxis]
>>> b
array([[ 4873.40374783,  4873.40374783],
       [ 5821.07686377,  5821.07686377],
       [ 5781.99852348,  5781.99852348],
       [ 5555.53769711,  5555.53769711],
       [    0.        ,     0.        ],
       [    0.        ,     0.        ],
       [    0.        ,     0.        ],
       [    0.        ,     0.        ]])
>>> b.sum(0)[0] == b[:,0].sum()
False

>>> b.sum(0)[0]
22032.016832190002

>>> b[:,0].sum()
22032.016832189998