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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_edges(self):
 """Get the edges for the current surface. If they haven't been computed yet, first compute and store them. This is provided as a means for internal calls to get the edges without copying (since :attr:`.edges` copies before giving to a user to keep the stored data immutable). Returns: Tuple[~bezier.curve.Curve, ~bezier.curve.Curve, \ ~bezier.curve.Curve]: The edges of the surface. """

        if self._edges is None:
            self._edges = self._compute_edges()
        return self._edges