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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 visit_list(self, node, *args, **kwargs):
 """As transformers may return lists in some places this method can be used to enforce a list as return value. """

        rv = self.visit(node, *args, **kwargs)
        if not isinstance(rv, list):
            rv = [rv]
        return rv