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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 _compile_pfgen(self):
 """Post power flow computation for PV and SW"""

        string = '"""\n'
        string += 'system.dae.init_g()\n'
        for gcall, pflow, shunt, series, stagen, call in zip(
                self.gcall, self.pflow, self.shunt, self.series, self.stagen,
                self.gcalls):
            if gcall and pflow and (shunt or series) and not stagen:
                string += call
        string += '\n'
        string += 'system.dae.reset_small_g()\n'
        string += '"""'
        self.pfgen = compile(eval(string), '', 'exec')