Replace DAGNode class with OpNode, InNode, and OutNode classes

qiskit/dagcircuit/__init__.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2017.
+# (C) Copyright IBM 2017, 2021.
 #
 # 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
@@ -25,6 +25,9 @@
 
    DAGCircuit
    DAGNode
+   OpNode
+   InNode
+   OutNode
    DAGDepNode
    DAGDependency
 
@@ -37,7 +40,7 @@
    DAGCircuitError
 """
 from .dagcircuit import DAGCircuit
-from .dagnode import DAGNode
+from .dagnode import DAGNode, OpNode, InNode, OutNode
 from .dagdepnode import DAGDepNode
 from .exceptions import DAGCircuitError
 from .dagdependency import DAGDependency

qiskit/dagcircuit/dagnode.py

@@ -1,6 +1,6 @@
 # This code is part of Qiskit.
 #
-# (C) Copyright IBM 2017, 2019.
+# (C) Copyright IBM 2017, 2019, 2021.
 #
 # 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
@@ -12,25 +12,37 @@
 
 # pylint: disable=redefined-builtin
 
-"""Object to represent the information at a node in the DAGCircuit."""
+"""Objects to represent the information at a node in the DAGCircuit."""
 
 import warnings
 
 from qiskit.exceptions import QiskitError
 
 
 class DAGNode:
-    """Object to represent the information at a node in the DAGCircuit.
-
-    It is used as the return value from `*_nodes()` functions and can
-    be supplied to functions that take a node.
-    """
+    """Parent class for OpNode, InNode, and OutNode."""
 
     __slots__ = ["type", "_op", "_qargs", "cargs", "_wire", "sort_key", "_node_id"]
 
     def __init__(self, type=None, op=None, name=None, qargs=None, cargs=None, wire=None, nid=-1):
         """Create a node"""
+        if type is not None:
+            warnings.warn(
+                "The DAGNode 'type' attribute is deprecated as of 0.18.0 and "
+                "will be removed no earlier than 3 months after the release date. "
+                "Use OpNode, InNode, or OutNode instead of DAGNode.",
+                DeprecationWarning,
+                2,
+            )
         self.type = type
+        if op is not None:
+            warnings.warn(
+                "The DAGNode 'op' attribute is deprecated as of 0.18.0 and "
+                "will be removed no earlier than 3 months after the release date."
+                "Use OpNode instead of DAGNode.",
+                DeprecationWarning,
+                2,
+            )
         self._op = op
         if name is not None:
             warnings.warn(
@@ -42,6 +54,14 @@ def __init__(self, type=None, op=None, name=None, qargs=None, cargs=None, wire=N
             )
         self._qargs = qargs if qargs is not None else []
         self.cargs = cargs if cargs is not None else []
+        if wire is not None:
+            warnings.warn(
+                "The DAGNode 'wire' attribute is deprecated as of 0.18.0 and "
+                "will be removed no earlier than 3 months after the release date."
+                "Use InNode or OutNode instead of DAGNode.",
+                DeprecationWarning,
+                2,
+            )
         self._wire = wire
         self._node_id = nid
         self.sort_key = str(self._qargs)
@@ -61,13 +81,14 @@ def op(self, data):
     def name(self):
         """Returns the Instruction name corresponding to the op for this node"""
         if self.type and self.type == "op":
-            return self._op.name
+            return self.op.name
         return None
 
     @name.setter
     def name(self, name):
+        """Sets the Instruction name corresponding to the op for this node"""
         if self.type and self.type == "op":
-            self._op.name = name
+            self.op.name = name
 
     @property
     def condition(self):
@@ -81,7 +102,7 @@ def condition(self):
             DeprecationWarning,
             2,
         )
-        return self._op.condition
+        return self.op.condition
 
     @condition.setter
     def condition(self, new_condition):
@@ -95,7 +116,7 @@ def condition(self, new_condition):
             DeprecationWarning,
             2,
         )
-        self._op.condition = new_condition
+        self.op.condition = new_condition
 
     @property
     def qargs(self):
@@ -140,8 +161,8 @@ def semantic_eq(node1, node2, bit_indices1=None, bit_indices2=None):
         Check if DAG nodes are considered equivalent, e.g., as a node_match for nx.is_isomorphic.
 
         Args:
-            node1 (DAGNode): A node to compare.
-            node2 (DAGNode): The other node to compare.
+            node1 (OpNode, InNode, OutNode): A node to compare.
+            node2 (OpNode, InNode, OutNode): The other node to compare.
             bit_indices1 (dict): Dictionary mapping Bit instances to their index
                 within the circuit containing node1
             bit_indices2 (dict): Dictionary mapping Bit instances to their index
@@ -163,26 +184,93 @@ def semantic_eq(node1, node2, bit_indices1=None, bit_indices2=None):
             bit_indices1 = {arg: arg for arg in node1.qargs + node1.cargs}
             bit_indices2 = {arg: arg for arg in node2.qargs + node2.cargs}
 
-        node1_qargs = [bit_indices1[qarg] for qarg in node1.qargs]
-        node1_cargs = [bit_indices1[carg] for carg in node1.cargs]
-
-        node2_qargs = [bit_indices2[qarg] for qarg in node2.qargs]
-        node2_cargs = [bit_indices2[carg] for carg in node2.cargs]
-
-        # For barriers, qarg order is not significant so compare as sets
-        if "barrier" == node1.name == node2.name:
-            return set(node1_qargs) == set(node2_qargs)
-
-        if node1.type == node2.type:
-            if node1._op == node2._op:
-                if node1.name == node2.name:
-                    if node1_qargs == node2_qargs:
-                        if node1_cargs == node2_cargs:
-                            if node1.type == "op":
-                                if node1._op.condition != node2._op.condition:
-                                    return False
-                            if bit_indices1.get(node1._wire, None) == bit_indices2.get(
-                                node2._wire, None
-                            ):
-                                return True
+        if isinstance(node1, OpNode) and isinstance(node2, OpNode):
+            node1_qargs = [bit_indices1[qarg] for qarg in node1.qargs]
+            node1_cargs = [bit_indices1[carg] for carg in node1.cargs]
+
+            node2_qargs = [bit_indices2[qarg] for qarg in node2.qargs]
+            node2_cargs = [bit_indices2[carg] for carg in node2.cargs]
+
+            # For barriers, qarg order is not significant so compare as sets
+            if "barrier" == node1.op.name == node2.op.name:
+                return set(node1_qargs) == set(node2_qargs)
+
+            if node1_qargs == node2_qargs:
+                if node1_cargs == node2_cargs:
+                    if node1.op.condition == node2.op.condition:
+                        if node1.op == node2.op:
+                            return True
+        elif (isinstance(node1, InNode) and isinstance(node2, InNode)) or (
+            isinstance(node1, OutNode) and isinstance(node2, OutNode)
+        ):
+            if bit_indices1.get(node1.wire, None) == bit_indices2.get(node2.wire, None):
+                return True
+
         return False
+
+
+class OpNode(DAGNode):
+    """Object to represent an Instruction at a node in the DAGCircuit."""
+
+    __slots__ = ["op"]
+
+    def __init__(self, op, qargs=None, cargs=None):
+        """Create an Instruction node"""
+        self.op = op
+        super().__init__(qargs=qargs, cargs=cargs)
+
+    @property
+    def name(self):
+        """Returns the Instruction name corresponding to the op for this node"""
+        return self.op.name
+
+    @name.setter
+    def name(self, new_name):
+        """Sets the Instruction name corresponding to the op for this node"""
+        self.op.name = new_name
+
+    @property
+    def condition(self):
+        """Returns the condition of the node.op"""
+        warnings.warn(
+            "The OpNode 'condition' attribute is deprecated as of 0.18.0 and "
+            "will be removed no earlier than 3 months after the release date. "
+            "You can use 'OpNode.op.condition'.",
+            DeprecationWarning,
+            2,
+        )
+        return self.op.condition
+
+    @condition.setter
+    def condition(self, new_condition):
+        """Sets the node.condition which sets the node.op.condition."""
+        warnings.warn(
+            "The OpNode 'condition' attribute is deprecated as of 0.18.0 and "
+            "will be removed no earlier than 3 months after the release date. "
+            "You can use 'OpNode.op.condition'.",
+            DeprecationWarning,
+            2,
+        )
+        self.op.condition = new_condition
+
+
+class InNode(DAGNode):
+    """Object to represent an incoming wire node in the DAGCircuit."""
+
+    __slots__ = ["wire"]
+
+    def __init__(self, wire):
+        """Create an incoming node"""
+        self.wire = wire
+        super().__init__()
+
+
+class OutNode(DAGNode):
+    """Object to represent an outgoing wire node in the DAGCircuit."""
+
+    __slots__ = ["wire"]
+
+    def __init__(self, wire):
+        """Create an outgoing node"""
+        self.wire = wire
+        super().__init__()

qiskit/transpiler/passes/analysis/dag_longest_path.py

@@ -16,7 +16,7 @@
 
 
 class DAGLongestPath(AnalysisPass):
-    """Return the longest path in a DAGcircuit as a list of DAGNodes."""
+    """Return the longest path in a DAGcircuit as a list of OpNodes, InNodes, and OutNodes."""
 
     def run(self, dag):
         """Run the DAGLongestPath pass on `dag`."""

qiskit/transpiler/passes/layout/apply_layout.py

@@ -13,7 +13,7 @@
 """Transform a circuit with virtual qubits into a circuit with physical qubits."""
 
 from qiskit.circuit import QuantumRegister
-from qiskit.dagcircuit import DAGCircuit
+from qiskit.dagcircuit import DAGCircuit, OpNode
 from qiskit.transpiler.basepasses import TransformationPass
 from qiskit.transpiler.exceptions import TranspilerError
 
@@ -59,7 +59,7 @@ def run(self, dag):
         for creg in dag.cregs.values():
             new_dag.add_creg(creg)
         for node in dag.topological_op_nodes():
-            if node.type == "op":
+            if isinstance(node, OpNode):
                 qargs = [q[layout[qarg]] for qarg in node.qargs]
                 new_dag.apply_operation_back(node.op, qargs, node.cargs)
         new_dag._global_phase = dag._global_phase