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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def amalgamate(A, blocksize):
 """Amalgamate matrix A. Parameters A : csr_matrix Matrix to amalgamate blocksize : int blocksize to use while amalgamating Returns ------- A_amal : csr_matrix Amalgamated matrix A, first, convert A to BSR with square blocksize and then return a CSR matrix of ones using the resulting BSR indptr and indices Notes ----- inverse operation of UnAmal for square matrices Examples -------- matrix([[1, 0, 2, 0], [0, 3, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]) matrix([[ 1., 1.], [ 0., 0.]]) """

    if blocksize == 1:
        return A
    elif sp.mod(A.shape[0], blocksize) != 0:
        raise ValueError("Incompatible blocksize")

    A = A.tobsr(blocksize=(blocksize, blocksize))
    A.sort_indices()
    subI = (np.ones(A.indices.shape), A.indices, A.indptr)
    shape = (int(A.shape[0]/A.blocksize[0]),
             int(A.shape[1]/A.blocksize[1]))
    return csr_matrix(subI, shape=shape)