text: # -*- coding: utf-8 -*-
  
  # This code is part of Qiskit.
  #
  # (C) Copyright IBM 2017, 2018.
  #
  # This code is licensed under the Apache License, Version 2.0. You may
  # obtain a copy of this license in the LICENSE.txt file in the root directory
  # of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
  #
  # Any modifications or derivative works of this code must retain this
  # copyright notice, and modified files need to carry a notice indicating
  # that they have been altered from the originals.
  
  """Helper function for converting a circuit to a dag"""
  
  from qiskit.dagcircuit.dagcircuit import DAGCircuit
  
  
  def circuit_to_dag(circuit):
      """Build a ``DAGCircuit`` object from a ``QuantumCircuit``.
  
      Args:
          circuit (QuantumCircuit): the input circuit.
  
      Return:
          DAGCircuit: the DAG representing the input circuit.
      """
      dagcircuit = DAGCircuit()
      dagcircuit.name = circuit.name
      for register in circuit.qregs:
          dagcircuit.add_qreg(register)
      for register in circuit.cregs:
          dagcircuit.add_creg(register)
  
      for instruction, qargs, cargs in circuit.data:
          # Get arguments for classical control (if any)
          if instruction.control is None:
              control = None
          else:
              control = (instruction.control[0], instruction.control[1])
  
          dagcircuit.apply_operation_back(instruction.copy(),
                                          qargs, cargs, control)
  
      return dagcircuit
  