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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 camera(self):
 """ Get the single camera for the scene. If not manually set one will abe automatically generated. Returns camera : trimesh.scene.Camera Camera object defined for the scene """

        # no camera set for the scene yet
        if not hasattr(self, '_camera') or self._camera is None:
            # will create a camera with everything in view
            return self.set_camera()

        return self._camera