In [1]: import numpy as np

In [2]: a1 = np.zeros((2,3))

In [3]: a2 = np.ones((2,4))

In [5]: a = np.c_[a1,a2]

In [6]: a
Out[6]:
array([[ 0.,  0.,  0.,  1.,  1.,  1.,  1.],
       [ 0.,  0.,  0.,  1.,  1.,  1.,  1.]])