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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 delete_rows_csr(mat, indices):
 """ Remove the rows denoted by ``indices`` form the CSR sparse matrix ``mat``. """

    if not isinstance(mat, scipy.sparse.csr_matrix):
        raise ValueError("works only for CSR format -- use .tocsr() first")
    indices = list(indices)
    mask = np.ones(mat.shape[0], dtype=bool)
    mask[indices] = False
    return mat[mask]