<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _compile_bus_injection(self):
 """Impose injections on buses"""

        string = '"""\n'
        for device, series in zip(self.devices, self.series):
            if series:
                string += 'system.' + device + '.gcall(system.dae)\n'
        string += '\n'
        string += 'system.dae.reset_small_g()\n'
        string += self.gisland
        string += '"""'
        self.bus_injection = compile(eval(string), '', 'exec')