text: # 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.
  
  """Base transpiler passes."""
  
  from abc import abstractmethod
  from collections.abc import Hashable
  from inspect import signature
  from .propertyset import PropertySet
  
  
  class MetaPass(type):
      """Metaclass for transpiler passes.
  
      Enforces the creation of some fields in the pass while allowing passes to
      override ``__init__``.
      """
  
      def __call__(cls, *args, **kwargs):
          pass_instance = type.__call__(cls, *args, **kwargs)
          pass_instance._hash = hash(MetaPass._freeze_init_parameters(cls, args, kwargs))
          return pass_instance
  
      @staticmethod
      def _freeze_init_parameters(class_, args, kwargs):
          self_guard = object()
          init_signature = signature(class_.__init__)
          bound_signature = init_signature.bind(self_guard, *args, **kwargs)
          arguments = [('class_.__name__', class_.__name__)]
          for name, value in bound_signature.arguments.items():
              if value == self_guard:
                  continue
              if isinstance(value, Hashable):
                  arguments.append((name, type(value), value))
              else:
                  arguments.append((name, type(value), repr(value)))
          return frozenset(arguments)
  
  
  class BasePass(metaclass=MetaPass):
      """Base class for transpiler passes."""
  
      def __init__(self):
          self.requires = []  # List of passes that requires
          self.preserves = []  # List of passes that preserves
          self.property_set = PropertySet()  # This pass's pointer to the pass manager's property set.
          self._hash = None
  
      def __hash__(self):
          return self._hash
  
      def __eq__(self, other):
          return hash(self) == hash(other)
  
      def name(self):
          """Return the name of the pass."""
          return self.__class__.__name__
  
      @abstractmethod
      def run(self, dag):
          """Run a pass on the DAGCircuit. This is implemented by the pass developer.
  
          Args:
              dag (DAGCircuit): the dag on which the pass is run.
          Raises:
              NotImplementedError: when this is left unimplemented for a pass.
          """
          raise NotImplementedError
  
      @property
      def is_transformation_pass(self):
          """Check if the pass is a transformation pass.
  
          If the pass is a TransformationPass, that means that the pass can manipulate the DAG,
          but cannot modify the property set (but it can be read).
          """
          return isinstance(self, TransformationPass)
  
      @property
      def is_analysis_pass(self):
          """Check if the pass is an analysis pass.
  
          If the pass is an AnalysisPass, that means that the pass can analyze the DAG and write
          the results of that analysis in the property set. Modifications on the DAG are not allowed
          by this kind of pass.
          """
          return isinstance(self, AnalysisPass)
  
      def __call__(self, circuit, property_set=None):
          """Runs the pass on circuit.
  
          Args:
              circuit (QuantumCircuit): the dag on which the pass is run.
              property_set (PropertySet or dict or None): input/output property set. An analysis pass
                  might change the property set in-place.
  
          Returns:
              QuantumCircuit: If on transformation pass, the resulting QuantumCircuit. If analysis
                     pass, the input circuit.
          """
          from qiskit.converters import circuit_to_dag, dag_to_circuit
          from qiskit.dagcircuit.dagcircuit import DAGCircuit
  
          property_set_ = None
          if isinstance(property_set, dict):  # this includes (dict, PropertySet)
              property_set_ = PropertySet(property_set)
  
          if isinstance(property_set_, PropertySet):
              self.property_set = property_set_
  
          result = self.run(circuit_to_dag(circuit))
  
          result_circuit = circuit
  
          if isinstance(property_set, dict):  # this includes (dict, PropertySet)
              property_set.clear()
              property_set.update(self.property_set)
  
          if isinstance(result, DAGCircuit):
              result_circuit = dag_to_circuit(result)
  
          if result is None and self.property_set['layout']:
              result_circuit = circuit.copy()
              result_circuit._layout = self.property_set['layout']
  
          return result_circuit
  
  
  class AnalysisPass(BasePass):  # pylint: disable=abstract-method
      """An analysis pass: change property set, not DAG."""
      pass
  
  
  class TransformationPass(BasePass):  # pylint: disable=abstract-method
      """A transformation pass: change DAG, not property set."""
      pass
  