Issue 6633: Update _parameter_table after circuit assignment

qiskit/circuit/quantumcircuitdata.py

@@ -17,6 +17,7 @@
 
 from qiskit.circuit.exceptions import CircuitError
 from qiskit.circuit.instruction import Instruction
+from .parameter import Parameter
 
 
 class QuantumCircuitData(MutableSequence):
@@ -54,10 +55,46 @@ def __setitem__(self, key, value):
         self._circuit._check_qargs(qargs)
         self._circuit._check_cargs(cargs)
 
+        circ_data = {}
+        param = {"old": 0, "new": 0}
+        circ_data["old"] = self._circuit._data
         self._circuit._data[key] = (instruction, qargs, cargs)
+        circ_data["new"] = self._circuit._data
 
         self._circuit._update_parameter_table(instruction)
 
+        if len(circ_data["old"][key][0].params) > 0:
+            if isinstance(circ_data["old"][key][0].params[0], Parameter):
+                param["old"] = circ_data["old"][key][0].params[0]
+
+        if len(circ_data["new"][key][0].params) > 0:
+            if isinstance(circ_data["new"][key][0].params[0], Parameter):
+                param["new"] = circ_data["new"][key][0].params[0]
+
+        param_count = -1
+        if isinstance(param["old"], Parameter):
+            for idx, data in enumerate(circ_data["old"]):
+                if idx <= key:
+                    if len(data[0].params) > 0:
+                        if data[0].params[0] == param["old"]:
+                            param_count = param_count + 1
+                else:
+                    pass
+            self._circuit._parameter_table[param["old"]].pop(param_count)
+
+        param_count = -1
+        if isinstance(param["new"], Parameter):
+            for idx, data in enumerate(circ_data["new"]):
+                if idx <= key:
+                    if len(data[0].params) > 0:
+                        if data[0].params[0] == param["new"]:
+                            param_count = param_count + 1
+                else:
+                    pass
+            added_element = self._circuit._parameter_table[param["new"]][-1]
+            self._circuit._parameter_table[param["new"]].insert(param_count, added_element)
+            self._circuit._parameter_table[param["new"]].pop()
+
     def insert(self, index, value):
         self._circuit._data.insert(index, None)
         self[index] = value

qiskit/test/base.py

@@ -62,6 +62,7 @@ class BaseTestCase(testtools.TestCase):
         assertRaises = unittest.TestCase.assertRaises
         assertEqual = unittest.TestCase.assertEqual
 
+
 else:
 
     class BaseTestCase(unittest.TestCase):

releasenotes/notes/parameter-table-updated-after-circuit-assignment-61bae00b33f8cf40.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed a bug when ``QuantumCircuit._parameter_table`` is inconsistent with
+    ``QuantumCircuit.data`` after a circuit assignment.
+    In __setitem__ of QuantumCiruitData, for each new entry, the old element 
+    is removed and the new element is added properly.

test/python/circuit/test_circuit_data.py

@@ -425,3 +425,19 @@ def test_param_gate_instance(self):
         qc0_instance = qc0._parameter_table[b][0][0]
         qc1_instance = qc1._parameter_table[a][0][0]
         self.assertNotEqual(qc0_instance, qc1_instance)
+
+    def test_parameter_table_is_updated(self):
+        """Verify that circuit._parameter_table is consistent with circuit.data."""
+        qr = QuantumRegister(1, "q")
+        qc = QuantumCircuit(qr)
+
+        a = Parameter("a")
+        qc.h(0)
+        qc.ry(a, 0)
+        qc.rz(a, 0)
+
+        qc.data[0] = (RXGate(a), [qr[0]], [])
+        qc.data[1] = (RXGate(a), [qr[0]], [])
+        qc.data[2] = (HGate(), [qr[0]], [])
+
+        qc.copy()