parameterless support

qiskit/transpiler/passes/optimization/unroll_forloops.py

@@ -45,7 +45,7 @@ def run(self, dag):
             DAGCircuit: Transformed DAG.
         """
         for forloop_op in dag.op_nodes(ForLoopOp):
-            (indexset, loop_parameter, body) = forloop_op.op.params
+            (indexset, loop_param, body) = forloop_op.op.params
 
             # skip unrolling if it results in bigger than max_target_depth
             if self.max_target_depth > 0 and len(indexset) * body.depth() > self.max_target_depth:
@@ -57,8 +57,8 @@ def run(self, dag):
 
             unrolled_dag = circuit_to_dag(body).copy_empty_like()
             for index_value in indexset:
-                bound_body_dag = circuit_to_dag(body.bind_parameters({loop_parameter: index_value}))
-                unrolled_dag.compose(bound_body_dag, inplace=True)
+                bound_body = body.bind_parameters({loop_param: index_value}) if loop_param else body
+                unrolled_dag.compose(circuit_to_dag(bound_body), inplace=True)
             dag.substitute_node_with_dag(forloop_op, unrolled_dag)
 
         return dag

test/python/transpiler/test_unroll_forloops.py

@@ -46,6 +46,28 @@ def test_range(self):
 
         self.assertEqual(result, expected)
 
+    def test_parameterless_range(self):
+        """Check simples unrolling case when there is not parameter"""
+        qreg, creg = QuantumRegister(5, "q"), ClassicalRegister(2, "c")
+
+        body = QuantumCircuit(3, 1)
+        indexset = range(0, 10, 2)
+
+        body.h([0, 1, 2])
+
+        circuit = QuantumCircuit(qreg, creg)
+        circuit.for_loop(indexset, None, body, [1, 2, 3], [1])
+
+        expected = QuantumCircuit(qreg, creg)
+        for _ in indexset:
+            expected.h([1, 2, 3])
+
+        passmanager = PassManager()
+        passmanager.append(UnrollForLoops())
+        result = passmanager.run(circuit)
+
+        self.assertEqual(result, expected)
+
     def test_skip_continue_loop(self):
         """Unrolling should not be done when a `continue;` in the body"""
         parameter = Parameter("x")