human
Solve the following python programming problem given the following code:
def ancestors(variable_list, blockers = None) : 
    '
    Return the variables that contribute to those in variable_list (inclusive).

    Parameters
    ----------
    variable_list : list of `Variable` instances
        Output `Variable` instances from which to search backward through
        owners.

    Returns
    -------
    list of `Variable` instances
        All input nodes, in the order found by a left-recursive depth-first
        search started at the nodes in `variable_list`.

    ' 
    def expand(r) : 
        if (r.owner and ((not blockers) or (r not in blockers))) : 
            return reversed (r.owner.inputs) 
dfs_variables = stack_search (deque (variable_list), expand, 'dfs') 
    return blockers 

    
    

    Fix the buggy line: return blockers
assistant
#Here is Python code to fix the buggy line: return blockers
.

return dfs_variables