code: def _energy_evaluation(self, operator):
          
          if self._quantum_state is not None:
              input_circuit = self._quantum_state
          else:
              input_circuit = [self.opt_circuit]
          if operator._paulis:
              mean_energy, std_energy = operator.evaluate_with_result(self._operator_mode, input_circuit,
                                                                      self._quantum_instance.backend, self.ret)
          else:
              mean_energy = 0.0
              std_energy = 0.0
          operator.disable_summarize_circuits()
          logger.debug('Energy evaluation {} returned {}'.format(self._eval_count, np.real(mean_energy)))
          return np.real(mean_energy), np.real(std_energy)
docs: Evaluate the energy of the current input circuit with respect to the given operator.
  
          :param operator: Hamiltonian of the system
  
          :return: Energy of the Hamiltonian