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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 compute_flows(self):
 """ If enabled, compute the line flows after each step Returns ------- None """

        system = self.system
        config = self.config
        dae = system.dae

        if config.compute_flows:
            # compute and append series injections on buses

            exec(system.call.bus_injection)
            bus_inj = dae.g[:2 * system.Bus.n]

            exec(system.call.seriesflow)
            system.Area.seriesflow(system.dae)
            system.Area.interchange_varout()
            dae.y = matrix([
                dae.y, bus_inj, system.Line._line_flows, system.Area.inter_varout
            ])