human
Solve the following python programming problem given the following code:
def test_select_y() : 
    def _check(data, expected, aggregator = None) : 
        v = api.Viz (data) 
        v.encode () 
        v.encoding.x = 'col1' 
        if (aggregator is None) : 
            v.select_y () 
            assert (v.encoding.y.name == expected) 
else : 
            v.select_y (None, aggregator) 
            assert (v.encoding.y.name == expected) 
            assert (v.encoding.y.aggregate == aggregator) 
data = dict (col1 = [1.0, 2.0, 3.0], col2 = ['A', 'B', 'C'], col3 = pd.date_range ('2012', periods = 3, freq = 'A'), col4 = pd.date_range ('2012', periods = 3, freq = 'A'), col5 = [1.0, 2.0, 3.0], col6 = [1.0, 2.0, 3.0]) 
    _check (data, 'col5') 
    _check (data, 'col5', 'avg') 
    data = dict (col1 = [1.0, 2.0, 3.0], col2 = ['A', 'B', 'C'], col3 = pd.date_range ('2012', periods = 3, freq = 'A'), col4 = ['A', 'B', 'C']) 
    _check (data, 'col2') 
    _check (data, 'col2', 'sum') 
    data = dict (col1 = [1.0, 2.0, 3.0], col2 = pd.date_range ('2012', periods = 3, freq = 'A'), col3 = pd.date_range ('2012', periods = 3, freq = 'A')) 
    _check (data, 'col2') 
    _check (v, 'col2', 'sum') 
    with pytest.raises (AssertionError) : 
        v = api.Viz (None) 
        v.select_y () 
with pytest.raises (AssertionError) : 
        v = api.Viz (dict (col1 = [1.0, 2.0])) 
        v.select_y () 
with pytest.raises (AssertionError) : 
        v = api.Viz (dict (col1 = [1.0, 2.0], col2 = [1.0, 2.0])) 
        v.select_y () 
with pytest.raises (AssertionError) : 
        v = api.Viz (dict (col1 = [1.0, 2.0], col2 = [1.0, 2.0])) 
        v.encode () 
        v.select_y () 
data = dict (col1 = [1.0, 2.0, 3.0], col2 = ['A', 'B', 'C'], col3 = pd.date_range ('2012', periods = 3, freq = 'A'), col4 = pd.date_range ('2012', periods = 3, freq = 'A'), col5 = [1.0, 2.0, 3.0], col6 = [1.0, 2.0, 3.0]) 
    v = api.Viz (data) 
    v.encode () 
    v.encoding.x = 'col1' 
    v.select_y (['N', 'T', 'Q', 'O']) 
    assert (v.encoding.y.name == 'col2') 

    
    

    Fix the buggy line: _check (v, 'col2', 'sum')
assistant
#Here is Python code to fix the buggy line: _check (v, 'col2', 'sum')
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_check (data, 'col2', 'sum')