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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 _create_injector(self, injector):
 """Returns a new batch injector"""

        if injector == "block_info":
            block_info_injector = importlib.import_module(
                "sawtooth_validator.journal.block_info_injector")

            return block_info_injector.BlockInfoInjector(
                self._state_view_factory, self._signer)

        raise UnknownBatchInjectorError(injector)