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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def traverse_by(self, fixers, traversal):
 """Traverse an AST, applying a set of fixers to each node. This is a helper method for refactor_tree(). Args: fixers: a list of fixer instances. traversal: a generator that yields AST nodes. Returns: None """

        if not fixers:
            return
        for node in traversal:
            for fixer in fixers[node.type]:
                results = fixer.match(node)
                if results:
                    new = fixer.transform(node, results)
                    if new is not None:
                        node.replace(new)
                        node = new