Operation abstract base class

qiskit/circuit/__init__.py

@@ -220,6 +220,7 @@
 from .controlledgate import ControlledGate
 from .instruction import Instruction
 from .instructionset import InstructionSet
+from .circuit_element import CircuitElement
 from .barrier import Barrier
 from .delay import Delay
 from .measure import Measure

qiskit/circuit/circuit_element.py

@@ -0,0 +1,49 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2017.
+#
+# 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.
+
+"""Circuit Element Mixin."""
+
+from abc import ABC, abstractmethod
+
+
+class CircuitElement(ABC):
+    """Circuit Element Mixin Class."""
+
+    @property
+    @abstractmethod
+    def name(self):
+        """Unique string identifier for operation type."""
+        raise NotImplementedError
+
+    @property
+    @abstractmethod
+    def num_qubits(self):
+        """Number of qubits."""
+        raise NotImplementedError
+
+    @property
+    @abstractmethod
+    def num_clbits(self):
+        """Number of classical bits."""
+        raise NotImplementedError
+
+    @property
+    @abstractmethod
+    def num_params(self):
+        """Number of parameters."""
+        raise NotImplementedError
+
+    @property
+    @abstractmethod
+    def params(self):
+        """List of parameters to specialize a specific CircuitElement instance."""
+        raise NotImplementedError

qiskit/circuit/instruction.py

@@ -42,11 +42,12 @@
 from qiskit.qobj.qasm_qobj import QasmQobjInstruction
 from qiskit.circuit.parameter import ParameterExpression
 from .tools import pi_check
+from .circuit_element import CircuitElement
 
 _CUTOFF_PRECISION = 1e-10
 
 
-class Instruction:
+class Instruction(CircuitElement):
     """Generic quantum instruction."""
 
     # Class attribute to treat like barrier for transpiler, unroller, drawer
@@ -75,9 +76,9 @@ def __init__(self, name, num_qubits, num_clbits, params, duration=None, unit="dt
             raise CircuitError(
                 "bad instruction dimensions: %d qubits, %d clbits." % num_qubits, num_clbits
             )
-        self.name = name
-        self.num_qubits = num_qubits
-        self.num_clbits = num_clbits
+        self._name = name
+        self._num_qubits = num_qubits
+        self._num_clbits = num_clbits
 
         self._params = []  # a list of gate params stored
         # Custom instruction label
@@ -430,7 +431,7 @@ def copy(self, name=None):
         cpy = self.__deepcopy__()
 
         if name:
-            cpy.name = name
+            cpy._name = name
         return cpy
 
     def __deepcopy__(self, _memo=None):
@@ -528,3 +529,43 @@ def repeat(self, n):
             qc.data = [(self, qargs[:], cargs[:])] * n
         instruction.definition = qc
         return instruction
+
+    @property
+    def name(self):
+        """Unique string identifier for operation type."""
+        return self._name
+
+    @name.setter
+    def name(self, name):
+        """Set the name."""
+        self._name = name
+
+    @property
+    def num_qubits(self):
+        """Number of qubits."""
+        return self._num_qubits
+
+    @num_qubits.setter
+    def num_qubits(self, num_qubits):
+        """Set num_qubits."""
+        self._num_qubits = num_qubits
+
+    @property
+    def num_clbits(self):
+        """Number of classical bits."""
+        return self._num_clbits
+
+    @num_clbits.setter
+    def num_clbits(self, num_clbits):
+        """Set num_clbits."""
+        self._num_clbits = num_clbits
+
+    @property
+    def num_params(self):
+        """Number of parameters."""
+        return self._num_params
+
+    @num_params.setter
+    def num_params(self, num_params):
+        """Set num_params."""
+        self._num_params = num_params

qiskit/circuit/instructionset.py

@@ -14,8 +14,8 @@
 Instruction collection.
 """
 from qiskit.circuit.exceptions import CircuitError
-from .instruction import Instruction
 from .classicalregister import Clbit
+from .circuit_element import CircuitElement
 
 
 class InstructionSet:
@@ -46,8 +46,8 @@ def __getitem__(self, i):
 
     def add(self, gate, qargs, cargs):
         """Add an instruction and its context (where it is attached)."""
-        if not isinstance(gate, Instruction):
-            raise CircuitError("attempt to add non-Instruction" + " to InstructionSet")
+        if not isinstance(gate, CircuitElement):
+            raise CircuitError("attempt to add non-CircuitElement" + " to InstructionSet")
         self.instructions.append(gate)
         self.qargs.append(qargs)
         self.cargs.append(cargs)

qiskit/circuit/quantumcircuit.py

@@ -56,6 +56,7 @@
 from .delay import Delay
 from .measure import Measure
 from .reset import Reset
+from .circuit_element import CircuitElement
 
 try:
     import pygments
@@ -1124,7 +1125,7 @@ def cbit_argument_conversion(self, clbit_representation: ClbitSpecifier) -> List
 
     def append(
         self,
-        instruction: Instruction,
+        instruction: CircuitElement,
         qargs: Optional[Sequence[QubitSpecifier]] = None,
         cargs: Optional[Sequence[ClbitSpecifier]] = None,
     ) -> InstructionSet:
@@ -1144,7 +1145,9 @@ def append(
             CircuitError: if object passed is neither subclass nor an instance of Instruction
         """
         # Convert input to instruction
-        if not isinstance(instruction, Instruction) and not hasattr(instruction, "to_instruction"):
+        if not isinstance(instruction, CircuitElement) and not hasattr(
+            instruction, "to_instruction"
+        ):
             if issubclass(instruction, Instruction):
                 raise CircuitError(
                     "Object is a subclass of Instruction, please add () to "
@@ -1154,7 +1157,7 @@ def append(
             raise CircuitError(
                 "Object to append must be an Instruction or have a to_instruction() method."
             )
-        if not isinstance(instruction, Instruction) and hasattr(instruction, "to_instruction"):
+        if not isinstance(instruction, CircuitElement) and hasattr(instruction, "to_instruction"):
             instruction = instruction.to_instruction()
 
         # Make copy of parameterized gate instances
@@ -1172,7 +1175,7 @@ def append(
         return instructions
 
     def _append(
-        self, instruction: Instruction, qargs: Sequence[Qubit], cargs: Sequence[Clbit]
+        self, instruction: CircuitElement, qargs: Sequence[Qubit], cargs: Sequence[Clbit]
     ) -> Instruction:
         """Append an instruction to the end of the circuit, modifying
         the circuit in place.
@@ -1189,8 +1192,8 @@ def _append(
             CircuitError: if the gate is of a different shape than the wires
                 it is being attached to.
         """
-        if not isinstance(instruction, Instruction):
-            raise CircuitError("object is not an Instruction.")
+        if not isinstance(instruction, CircuitElement):
+            raise CircuitError("object is not a CircuitElement.")
 
         # do some compatibility checks
         self._check_dups(qargs)

qiskit/quantum_info/operators/symplectic/clifford.py

@@ -16,7 +16,7 @@
 import numpy as np
 
 from qiskit.exceptions import QiskitError
-from qiskit.circuit import QuantumCircuit, Instruction
+from qiskit.circuit import QuantumCircuit, Instruction, CircuitElement
 from qiskit.circuit.library.standard_gates import IGate, XGate, YGate, ZGate, HGate, SGate
 from qiskit.quantum_info.operators.base_operator import BaseOperator
 from qiskit.quantum_info.operators.operator import Operator
@@ -27,7 +27,7 @@
 from .clifford_circuits import _append_circuit
 
 
-class Clifford(BaseOperator, AdjointMixin):
+class Clifford(BaseOperator, AdjointMixin, CircuitElement):
     """An N-qubit unitary operator from the Clifford group.
 
     **Representation**
@@ -525,6 +525,24 @@ def _pad_with_identity(self, clifford, qargs):
 
         return padded
 
+    # These implement the required methods of the CircuitElement mixin
+
+    @property
+    def name(self):
+        return "clifford"
+
+    @property
+    def num_params(self):
+        return 1
+
+    @property
+    def num_clbits(self):
+        return 0
+
+    @property
+    def params(self):
+        return (self._table,)
+
 
 # Update docstrings for API docs
 generate_apidocs(Clifford)