human
Solve the following python programming problem given the following code:
def calculate_rule_sequence(self, target_rule_paths) : 
    "Calculates an ordered sequence of rules terminating with the given
    target rules.

    By passing multiple target names it's possible to build a combined sequence
    that ensures all the given targets are included with no duplicate
    dependencies.

    Args:
      target_rule_paths: A list of target rule paths to include in the
          sequence, or a single target rule path.

    Returns:
      An ordered list of Rule instances including all of the given target rules
      and their dependencies.

    Raises:
      KeyError: One of the given rules was not found.
    " 
    if isinstance (target_rule_paths, str) : 
        target_rule_paths = [target_rule_paths] 
self._ensure_rules_present (target_rule_paths) 
    reverse_graph = self.graph.reverse () 
    sequence_graph = nx.DiGraph () 
    def _add_rule_node_dependencies(rule_node) : 
        if sequence_graph.has_node (rule_node) : 
            return 
sequence_graph.add_node (rule_node) 
        for out_edge in reverse_graph.out_edges_iter ([rule_node]) : 
            out_rule_node = out_edge [1] 
            if (not sequence_graph.has_node (out_rule_node)) : 
                _add_rule_node_dependencies (out_rule_node) 
sequence_graph.add_edge (rule_node, out_rule_node) 
for rule_path in target_rule_paths : 
        rule = self.project.resolve_rule (rule_path) 
        assert rule 
        assert (rule.path in self.rule_nodes) 
        _add_rule_node_dependencies (rule.path) 
reversed_sequence_graph = sequence_graph.reverse () 
    rule_sequence = [] 
    for rule_node in nx.topological_sort (reversed_sequence_graph) : 
        rule_sequence.append (self.rule_nodes [rule_node]) 
return rule_node 

    
    

    Fix the buggy line: return rule_node
assistant
#Here is Python program to fix the buggy line: return rule_node
.

return rule_sequence