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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 fenceloader(self):
        '''fence loader by sysid'''
        if not self.target_system in self.fenceloader_by_sysid:
            self.fenceloader_by_sysid[self.target_system] = mavwp.MAVFenceLoader()
        return self.fenceloader_by_sysid[self.target_system]