text: # -*- coding: utf-8 -*-
  # pylint: disable=invalid-name
  
  # Copyright 2017 IBM RESEARCH. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # =============================================================================
  
  """
  Pauli Y (bit-phase-flip) gate.
  """
  from qiskit import CompositeGate
  from qiskit import Gate
  from qiskit import InstructionSet
  from qiskit import QuantumCircuit
  from qiskit import QuantumRegister
  from qiskit.extensions.standard import header  # pylint: disable=unused-import
  
  
  class YGate(Gate):
      """Pauli Y (bit-phase-flip) gate."""
  
      def __init__(self, qubit, circ=None):
          """Create new Y gate."""
          super().__init__("y", [], [qubit], circ)
  
      def qasm(self):
          """Return OPENQASM string."""
          qubit = self.arg[0]
          return self._qasmif("y %s[%d];" % (qubit[0].name, qubit[1]))
  
      def inverse(self):
          """Invert this gate."""
          return self  # self-inverse
  
      def reapply(self, circuit):
          """Reapply this gate to corresponding qubits in circ."""
          self._modifiers(circuit.y(self.arg[0]))
  
  
  def y(self, quantum_register):
      """Apply Y to q."""
      if isinstance(quantum_register, QuantumRegister):
          intructions = InstructionSet()
          for register in range(quantum_register.size):
              intructions.add(self.y((quantum_register, register)))
          return intructions
  
      self._check_qubit(quantum_register)
      return self._attach(YGate(quantum_register, self))
  
  
  QuantumCircuit.y = y
  CompositeGate.y = y
  