human
Solve the following python programming problem given the following code:
@ mock.patch.object (dataflow, 'reach_def_analysis') 
def testDefUseGCD(self, mock_reach_def) : 
    'Test def use with the GCD function above.' 
    n1 = self._CreateMockNode ('n1', 0, [(['a'], 'c'), (['b'], 'd')]) 
    n2 = self._CreateMockNode ('n2', 2, [(['c'], None)]) 
    n3 = self._CreateMockNode ('n3', 3, [(['d'], 'ret')]) 
    n4 = self._CreateMockNode ('n4', 4, [(['d'], None)]) 
    n5 = self._CreateMockNode ('n5', 5, [(['c', 'd'], None)]) 
    n6 = self._CreateMockNode ('n6', 6, [(['c', 'd'], 'c')]) 
    n7 = self._CreateMockNode ('n7', 7, [(['c', 'd'], 'd')]) 
    n8 = self._CreateMockNode ('n8', 8, [(['c'], 'ret')]) 
    n9 = self._CreateMockNode ('n9', 9, [(['ret'], None)]) 
    graph_mock = mock.create_autospec (graph.Graph) 
    graph_mock.rpo = [n8, n2, n3, n4, n5, n6, n7, n8, n9] 
    mock_analysis = mock_reach_def.return_value 
    mock_analysis.def_to_loc = { 
        'a' : set ([(- 1)]), 
        'b' : set ([(- 2)]), 
        'c' : set ([0, 6]), 
        'd' : set ([1, 7]), 
        'ret' : set ([3, 8]), 
} 
    mock_analysis.defs = { 
        n1 : { 
            'c' : set ([0]), 
            'd' : set ([1]), 
}, 
        n2 : { 
            
}, 
        n3 : { 
            'ret' : set ([3]), 
}, 
        n4 : { 
            
}, 
        n5 : { 
            
}, 
        n6 : { 
            'c' : set ([6]), 
}, 
        n7 : { 
            'd' : set ([7]), 
}, 
        n8 : { 
            'ret' : set ([8]), 
}, 
        n9 : { 
            
}, 
} 
    mock_analysis.R = { 
        n1 : set ([(- 2), (- 1)]), 
        n2 : set ([(- 2), (- 1), 0, 1]), 
        n3 : set ([(- 2), (- 1), 0, 1]), 
        n4 : set ([(- 2), (- 1), 0, 1]), 
        n5 : set ([(- 2), (- 1), 0, 1]), 
        n6 : set ([(- 2), (- 1), 0, 1]), 
        n7 : set ([(- 2), (- 1), 0, 1]), 
        n8 : set ([(- 2), (- 1), 0, 1, 6, 7]), 
        n9 : set ([(- 2), (- 1), 0, 1, 3, 6, 7, 8]), 
} 
    expected_du = { 
        ('a', (- 1)) : [0], 
        ('b', (- 2)) : [1], 
        ('c', 0) : [2, 5, 6, 7, 8], 
        ('c', 6)...

    
    

    Fix the buggy line: graph_mock.rpo = [n8, n2, n3, n4, n5, n6, n7, n8, n9]
assistant
#Here is Python code to fix the buggy line: graph_mock.

graph_mock.rpo = [n1, n2, n3, n4, n5, n6, n7, n8, n9]