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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 calculate_pore_volume(self):
 """ Return the intrinsic pore volume. Returns ------- :class:`float` The intrinsic pore volume. """

        self.pore_volume = sphere_volume(self.calculate_pore_diameter() / 2)
        self.properties['pore_volume'] = self.pore_volume
        return self.pore_volume