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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 cell_sides_angstrom(self):
 """Array of sizes of a unit cell in Angstroms. The value is determined from the ``'cella'`` entry in `header`. """

        return np.asarray(
            self.header['cella']['value'], dtype=float) / self.data_shape