human
Solve the following python programming problem given the following code:
@ SkipTest 
def test_hashed_column_mapping(self) : 
    'Test whether hashed columns are mapped to correct HC dimensions.' 
    def get_hc_dim(expr, column) : 
        'Return the mapped dimension in hyper cube.' 
        return expr.mapped_hc_dimensions [expr.hashed_columns.index (column)] 
def get_shuffle_producers(expr) : 
        ' Go two steps deeper in the tree, find shuffle producers.
            ' 
        ret = [child.input.input for child in expr.children ()] 
        return tuple (ret) 
triangular_join = testNaryJoin.get_phys_plan_root ('A(x,y,z):-R(x,y),S(y,z),T(z,x)', 64) 
    (shuffle_r, shuffle_s, shuffle_t) = get_shuffle_producers (triangular_join) 
    self.assertEqual (get_hc_dim (shuffle_r, 0), get_hc_dim (shuffle_t, 1)) 
    self.assertEqual (get_hc_dim (shuffle_r, 1), get_hc_dim (shuffle_s, 0)) 
    self.assertEqual (get_hc_dim (shuffle_s, 1), get_hc_dim (shuffle_t, 0)) 
    star_join = testNaryJoin.get_phys_plan_root ('A(x,y,z,p):-R(x,y),S(x,z),T(x,p)', 64) 
    (shuffle_r, shuffle_s, shuffle_t) = get_shuffle_producers (triangular_join) 
    self.assertEqual (get_hc_dim (shuffle_r, 0), get_hc_dim (shuffle_s, 0)) 
    self.assertEqual (get_hc_dim (shuffle_s, 0), get_hc_dim (shuffle_t, 0)) 

    
    

    Fix the buggy line: (shuffle_r, shuffle_s, shuffle_t) = get_shuffle_producers (triangular_join)
assistant
#Here is Python code to find shuffle producers.

(shuffle_r, shuffle_s, shuffle_t) = get_shuffle_producers (star_join)