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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 normals(self, cells=False):
 """Retrieve vertex normals as a numpy array. :params bool cells: if `True` return cell normals. """

        if cells:
            vtknormals = self.polydata(True).GetCellData().GetNormals()
        else:
            vtknormals = self.polydata(True).GetPointData().GetNormals()
        return vtk_to_numpy(vtknormals)