Fix legacy deserialization

changes.d/696.fix

@@ -0,0 +1 @@
+`ConstantPulseTemplate`s from all versions can now be deserialized.

qupulse/pulses/constant_pulse_template.py

@@ -66,6 +66,15 @@ def get_serialization_data(self, serializer=None) -> Any:
         })
         return data
 
+    @classmethod
+    def deserialize(cls, serializer: Optional = None, **kwargs) -> 'ConstantPulseTemplate':
+        assert serializer is None, f"{cls} does not support legacy deserialization"
+        # this is for backwards compatible deserialization.
+        amplitudes = kwargs.pop('#amplitudes', None)
+        if amplitudes is not None:
+            kwargs['amplitude_dict'] = amplitudes
+        return cls(**kwargs)
+
     @property
     def integral(self) -> Dict[ChannelID, ExpressionScalar]:
         """Returns an expression giving the integral over the pulse."""

tests/pulses/constant_pulse_template_tests.py

@@ -10,6 +10,7 @@
 from qupulse._program._loop import make_compatible
 from qupulse._program.waveforms import ConstantWaveform
 
+from qupulse.serialization import DictBackend, PulseStorage
 from qupulse.pulses.constant_pulse_template import ConstantPulseTemplate, ExpressionScalar, TimeType
 
 from tests.serialization_tests import SerializableTests
@@ -164,3 +165,24 @@ def assert_equal_instance_except_id(self, lhs: ConstantPulseTemplate, rhs: Const
         self.assertEqual(lhs.measurement_declarations, rhs.measurement_declarations)
         self.assertEqual(lhs._amplitude_dict, rhs._amplitude_dict)
         self.assertEqual(lhs.duration, rhs.duration)
+
+    def test_legacy_deserialization(self):
+        serialized = """{
+            "#amplitudes": {
+                "ZI0_A_MARKER_FRONT": 1
+            },
+            "#type": "qupulse.pulses.constant_pulse_template.ConstantPulseTemplate",
+            "duration": 62848.0,
+            "name": "constant_pulse"
+        }"""
+        backend = DictBackend()
+        backend.storage['my_pt'] = serialized
+
+        ps = PulseStorage(backend)
+
+        deserialized = ps['my_pt']
+        expected = ConstantPulseTemplate(
+            amplitude_dict={"ZI0_A_MARKER_FRONT": 1},
+            duration=62848, name="constant_pulse"
+        )
+        self.assert_equal_instance(expected, deserialized)