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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 map_constructor(self, loader, node, deep=False):
 """ Walk the mapping, recording any duplicate keys. """

        mapping = {}
        for key_node, value_node in node.value:
            key = loader.construct_object(key_node, deep=deep)
            value = loader.construct_object(value_node, deep=deep)
            if key in mapping:
                raise ValueError(f"Duplicate key: \"{key}\"")
            mapping[key] = value

        return mapping