Add singledispatchmethod to dependency (#8944)

* add singledispatchmethod to dependency

* Fixup release note

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/circuit/classicalfunction/__init__.py

@@ -96,6 +96,13 @@ Exceptions
    ClassicalFunctionCompilerTypeError
 
 """
+
+from qiskit.utils import optionals as _optionals
+
+_optionals.HAS_TWEEDLEDUM.require_now("classical oracle creation")
+
+# pylint: disable=wrong-import-position
+
 from .classicalfunction import ClassicalFunction
 from .exceptions import (
     ClassicalFunctionParseError,

qiskit/transpiler/passes/basis/basis_translator.py

@@ -14,12 +14,12 @@
 
 """Translates gates to a target basis using a given equivalence library."""
 
+import sys
 import time
 import logging
 
 from itertools import zip_longest
 from collections import defaultdict
-from functools import singledispatch
 
 import retworkx
 
@@ -30,6 +30,10 @@ from qiskit.circuit.equivalence import Key
 from qiskit.transpiler.basepasses import TransformationPass
 from qiskit.transpiler.exceptions import TranspilerError
 
+if sys.version_info >= (3, 8):
+    from functools import singledispatchmethod  # pylint: disable=no-name-in-module
+else:
+    from singledispatchmethod import singledispatchmethod
 
 logger = logging.getLogger(__name__)
 
@@ -123,7 +127,7 @@ class BasisTranslator(TransformationPass):
         if self._target is None:
             basic_instrs = ["measure", "reset", "barrier", "snapshot", "delay"]
             target_basis = set(self._target_basis)
-            source_basis = set(_extract_basis(dag))
+            source_basis = set(self._extract_basis(dag))
             qargs_local_source_basis = {}
         else:
             basic_instrs = ["barrier", "snapshot"]
@@ -294,6 +298,29 @@ class BasisTranslator(TransformationPass):
         else:
             dag.substitute_node_with_dag(node, bound_target_dag)
 
+    @singledispatchmethod
+    def _extract_basis(self, circuit):
+        return circuit
+
+    @_extract_basis.register
+    def _(self, dag: DAGCircuit):
+        for node in dag.op_nodes():
+            if not dag.has_calibration_for(node):
+                yield (node.name, node.op.num_qubits)
+            if isinstance(node.op, ControlFlowOp):
+                for block in node.op.blocks:
+                    yield from self._extract_basis(block)
+
+    @_extract_basis.register
+    def _(self, circ: QuantumCircuit):
+        for instr_context in circ.data:
+            instr, _, _ = instr_context
+            if not circ.has_calibration_for(instr_context):
+                yield (instr.name, instr.num_qubits)
+            if isinstance(instr, ControlFlowOp):
+                for block in instr.blocks:
+                    yield from self._extract_basis(block)
+
     def _extract_basis_target(
         self, dag, qarg_indices, source_basis=None, qargs_local_source_basis=None
     ):
@@ -336,34 +363,6 @@ class BasisTranslator(TransformationPass):
         return source_basis, qargs_local_source_basis
 
 
-# this could be singledispatchmethod and included in above class when minimum
-# supported python version=3.8.
-@singledispatch
-def _extract_basis(circuit):
-    return circuit
-
-
-@_extract_basis.register
-def _(dag: DAGCircuit):
-    for node in dag.op_nodes():
-        if not dag.has_calibration_for(node):
-            yield (node.name, node.op.num_qubits)
-        if isinstance(node.op, ControlFlowOp):
-            for block in node.op.blocks:
-                yield from _extract_basis(block)
-
-
-@_extract_basis.register
-def _(circ: QuantumCircuit):
-    for instr_context in circ.data:
-        instr, _, _ = instr_context
-        if not circ.has_calibration_for(instr_context):
-            yield (instr.name, instr.num_qubits)
-        if isinstance(instr, ControlFlowOp):
-            for block in instr.blocks:
-                yield from _extract_basis(block)
-
-
 class StopIfBasisRewritable(Exception):
     """Custom exception that signals `retworkx.dijkstra_search` to stop."""
 

releasenotes/notes/add-singledispatchmethod-78ff14b1ef25ef99.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    For Python 3.7 `singledispatchmethod <https://pypi.org/project/singledispatchmethod/>`__
+    is now a dependency. This was added to enable leveraging the method dispatch
+    mechanism in the standard library of newer versions of Python. If you're on
+    Python >= 3.8 there is no extra dependency required.

requirements.txt

@@ -10,6 +10,7 @@ stevedore>=3.0.0
 symengine>=0.9 ; platform_machine == 'x86_64' or platform_machine == 'aarch64' or platform_machine == 'ppc64le' or platform_machine == 'amd64' or platform_machine == 'arm64'
 shared-memory38;python_version<'3.8'
 typing-extensions; python_version < '3.8'
+singledispatchmethod; python_version < '3.8'
 
 # To be removed as a requirement in Terra 0.23.  Tweedledum's wheels are
 # hopelessly broken on M1 mac, so we skip the waiting period for that.