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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 backward_substitution(matrix_u, matrix_y):
 """ Backward substitution method for the solution of linear systems. Solves the equation :math:`Ux = y` using backward substitution method where :math:`U` is a upper triangular matrix and :math:`y` is a column matrix. :param matrix_u: U, upper triangular matrix :type matrix_u: list, tuple :param matrix_y: y, column matrix :type matrix_y: list, tuple :return: x, column matrix :rtype: list """

    q = len(matrix_y)
    matrix_x = [0.0 for _ in range(q)]
    matrix_x[q - 1] = float(matrix_y[q - 1]) / float(matrix_u[q - 1][q - 1])
    for i in range(q - 2, -1, -1):
        matrix_x[i] = float(matrix_y[i]) - sum([matrix_u[i][j] * matrix_x[j] for j in range(i, q)])
        matrix_x[i] /= float(matrix_u[i][i])
    return matrix_x