I am concatenating a 1D numpy array to a 2D numpy array, but the code gives the following error:

*ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 2 dimensions. The detected shape was (2, 3) + inhomogeneous part.*

How can I fix this error?

Here is the code:

>>> import numpy as np

>>> a=np.array([[1,2,3],[4,5,6],[7,8,9]])

>>> b=np.array([10,11,12])

>>> np.concatenate([[a,b]])