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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 copy(self):
 """Return a shallow copy of this graph. """

        other = DirectedGraph()
        other._vertices = set(self._vertices)
        other._forwards = {k: set(v) for k, v in self._forwards.items()}
        other._backwards = {k: set(v) for k, v in self._backwards.items()}
        return other