class Site:

    def __init__(self, a):
        self.a = a

def set_a(self, new_a):
    self.a = new_a
vSite = np.vectorize(Site)
init_arry = np.arange(9).reshape((3, 3))
lattice = np.empty((3, 3), dtype=object)
lattice[:, :] = vSite(init_arry)
numpy array of objects