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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 rollback(self, label=None, plane='sdr'):
 """Rollback the configuration. This method rolls back the configuration on the device. Args: label (text):
 The configuration label ID plane: (text):
 sdr or admin Returns: A string with commit label or None """

        begin = time.time()
        rb_label = self._chain.target_device.rollback(label=label, plane=plane)
        elapsed = time.time() - begin
        if label:
            self.emit_message("Configuration rollback last {:.0f}s. Label: {}".format(elapsed, rb_label),
                              log_level=logging.INFO)
        else:
            self.emit_message("Configuration failed.", log_level=logging.WARNING)

        return rb_label