make wasm uid option in python

pytket/binders/circuit/Circuit/main.cpp

@@ -414,7 +414,15 @@ void def_circuit(py::class_<Circuit, std::shared_ptr<Circuit>> &pyCircuit) {
           "n_gates", &Circuit::n_gates,
           ":return: the number of gates in the Circuit")
       .def_property_readonly(
-          "wasm_uid", &Circuit::get_wasm_file_uid,
+          "wasm_uid",
+          [](const Circuit &circ) {
+            std::optional<std::string> result;
+            try {
+              result = circ.get_wasm_file_uid();
+            } catch (const std::exception &) {
+            }
+            return result;
+          },
           ":return: the unique wasm uid of the circuit")
       .def_property_readonly(
           "n_qubits", &Circuit::n_qubits,

pytket/pytket/_tket/circuit.pyi

@@ -2572,9 +2572,9 @@ class Circuit:
         A list of all qubit ids in the circuit
         """
     @property
-    def wasm_uid(self) -> str:
+    def wasm_uid(self) -> str | None:
         """
-        :return: the wasm uid of the first wasmop found in the circuit
+        :return: the unique wasm uid of the circuit
         """
 class ClBitVar:
     """

pytket/tests/classical_test.py

@@ -585,8 +585,7 @@ def test_wasm_uid_from_circuit_5() -> None:
     c = Circuit(0, 6)
 
     assert c.depth() == 0
-    with pytest.raises(ValueError):
-        c.wasm_uid
+    assert c.wasm_uid is None
 
 
 def test_wasm_append() -> None: