Error in find_coeffs function

[07Agarg]

res = np.dot(np.linalg.inv(A.T * A) * A.T, B)

What is the purpose of the above statement? It is giving an error: "numpy.linalg.linalg.LinAlgError: Singular matrix"

I tried using replacing np.linalg.inv with numpy.linalg.pinv. But still it is giving ValueError of shape inconsistency.

Thanks.