Move code for qasm for Instruction to QuantumCircuit

qiskit/circuit/instruction.py

@@ -584,26 +584,3 @@ def num_clbits(self):
     def num_clbits(self, num_clbits):
         """Set num_clbits."""
         self._num_clbits = num_clbits
-
-
-def _qasm(operation):
-    """Return a default OpenQASM string for the instruction.
-
-    Derived instructions may override this to print in a
-    different format (e.g. measure q[0] -> c[0];).
-    """
-    name_param = operation.name
-    if operation.params:
-        name_param = "{}({})".format(
-            name_param,
-            ",".join([pi_check(i, output="qasm", eps=1e-12) for i in operation.params]),
-        )
-    if operation.condition is not None:
-        if not isinstance(operation.condition[0], ClassicalRegister):
-            raise QasmError(
-                "OpenQASM 2 can only condition on registers, but got '{operation.condition[0]}'"
-            )
-        name_param = (
-            "if(%s==%d) " % (operation.condition[0].name, operation.condition[1]) + name_param
-        )
-    return name_param

qiskit/circuit/library/standard_gates/x.py

@@ -18,7 +18,6 @@
 from qiskit.utils.deprecation import deprecate_func
 from qiskit.circuit.controlledgate import ControlledGate
 from qiskit.circuit.gate import Gate
-import qiskit.circuit.instruction
 from qiskit.circuit.quantumregister import QuantumRegister
 from qiskit.circuit._utils import _compute_control_matrix, _ctrl_state_to_int
 from .h import HGate
@@ -588,7 +587,7 @@ def qasm(self):
         old_name = self.name
         self.name = "c3sqrtx"
         try:
-            return qiskit.circuit.instruction._qasm(self)
+            return qiskit.circuit._instruction_qasm(self)
         finally:
             self.name = old_name
 

qiskit/circuit/quantumcircuit.py

@@ -62,6 +62,7 @@
 from .delay import Delay
 from .measure import Measure
 from .reset import Reset
+from .tools import pi_check
 
 try:
     import pygments
@@ -1746,12 +1747,10 @@ def qasm(
                 operation = _qasm2_define_custom_operation(
                     operation, existing_gate_names, gates_to_define
                 )
-                if not isinstance(operation, Instruction):
-                    raise Exception(f"expecting Instruction got {type(operation)}")
                 # Insert qasm representation of the original instruction
                 if operation.name == "c3sx":
                     operation.name = "c3sqrtx"
-                name_param = qiskit.circuit.instruction._qasm(operation)
+                name_param = _instruction_qasm2(operation)
                 if operation.name == "c3sqrtx":
                     operation.name = "c3sx"
                 bits_qasm = ",".join(
@@ -5096,7 +5095,7 @@ def _qasm2_define_custom_operation(operation, existing_gate_names, gates_to_defi
                 instruction.operation, existing_gate_names, gates_to_define
             )
             bits_qasm = ",".join(qubit_labels[q] for q in instruction.qubits)
-            name_param = qiskit.circuit.instruction._qasm(new_operation)
+            name_param = _instruction_qasm2(new_operation)
             statements.append(f"{name_param} {bits_qasm};")
         body_qasm = " ".join(statements)
 
@@ -5211,3 +5210,21 @@ def _bit_argument_conversion_scalar(specifier, bit_sequence, bit_set, type_):
         else f"Invalid bit index: '{specifier}' of type '{type(specifier)}'"
     )
     raise CircuitError(message)
+
+def _instruction_qasm2(operation):
+    """Return an OpenQASM 2 string for the instruction."""
+    name_param = operation.name
+    if operation.params:
+        name_param = "{}({})".format(
+            name_param,
+            ",".join([pi_check(i, output="qasm", eps=1e-12) for i in operation.params]),
+        )
+    if operation.condition is not None:
+        if not isinstance(operation.condition[0], ClassicalRegister):
+            raise QasmError(
+                "OpenQASM 2 can only condition on registers, but got '{operation.condition[0]}'"
+            )
+        name_param = (
+            "if(%s==%d) " % (operation.condition[0].name, operation.condition[1]) + name_param
+        )
+    return name_param