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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 get_node_attribute(self, node, attribute_name):
 """Given a node and the name of an attribute, get a copy of that node's attribute. :param node: reference to the node to retrieve the attribute of. :param attribute_name: name of the attribute to retrieve. :returns: attribute value of the attribute_name key for the specified node. :raises: ValueError -- No such node exists. :raises: ValueError -- No such attribute exists. """

        if not self.has_node(node):
            raise ValueError("No such node exists.")
        elif attribute_name not in self._node_attributes[node]:
            raise ValueError("No such attribute exists.")
        else:
            return copy.\
                copy(self._node_attributes[node][attribute_name])