Fix VirtualTag (#3051)

quantumlib · May 31, 2020 · 008eab4 · 008eab4
1 parent caab356
commit 008eab4
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Showing 7 changed files with 17 additions and 3 deletions.
diff --git a/cirq/__init__.py b/cirq/__init__.py
@@ -262,6 +262,7 @@
     transform_op_tree,
     TwoQubitDiagonalGate,
     TwoQubitGate,
+    VirtualTag,
     WaitGate,
     X,
     XPowGate,

diff --git a/cirq/ops/tags.py b/cirq/ops/tags.py
@@ -12,9 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """Canonical tags for the TaggedOperation class."""
+from typing import Dict
 
 
-class VirtualTag():
+class VirtualTag:
     """A TaggedOperation tag indicating that the operation is virtual.
 
     Operations marked with this tag are presumed to have zero duration of their
@@ -29,4 +30,7 @@ def __str__(self) -> str:
         return '<virtual>'
 
     def __repr__(self) -> str:
-        return str(self)
+        return 'cirq.VirtualTag()'
+
+    def _json_dict_(self) -> Dict[str, str]:
+        return {'cirq_type': self.__class__.__name__}
diff --git a/cirq/ops/tags_test.py b/cirq/ops/tags_test.py
@@ -20,4 +20,7 @@ def test_virtual_tag():
     tag2 = cirq.ops.VirtualTag()
 
     assert tag1 == tag2
-    assert repr(tag1) == repr(tag2) == '<virtual>'
+    assert str(tag1) == str(tag2) == '<virtual>'
+
+    cirq.testing.assert_equivalent_repr(tag1)
+    cirq.testing.assert_equivalent_repr(tag2)
diff --git a/cirq/protocols/json_serialization.py b/cirq/protocols/json_serialization.py
@@ -147,6 +147,7 @@ def two_qubit_matrix_gate(matrix):
                 'TwoQubitDiagonalGate': cirq.TwoQubitDiagonalGate,
                 '_UnconstrainedDevice':
                 cirq.devices.unconstrained_device._UnconstrainedDevice,
+                'VirtualTag': cirq.VirtualTag,
                 'WaitGate': cirq.WaitGate,
                 '_QubitAsQid': raw_types._QubitAsQid,
                 'XPowGate': cirq.XPowGate,

diff --git a/cirq/protocols/json_test_data/VirtualTag.json b/cirq/protocols/json_test_data/VirtualTag.json
@@ -0,0 +1,3 @@
+{
+  "cirq_type": "VirtualTag"
+}
diff --git a/cirq/protocols/json_test_data/VirtualTag.repr b/cirq/protocols/json_test_data/VirtualTag.repr
@@ -0,0 +1 @@
+cirq.VirtualTag()
diff --git a/docs/api.rst b/docs/api.rst
@@ -138,6 +138,7 @@ the more general concept of a noisy open system quantum evolution.
     cirq.PhaseDampingChannel
     cirq.PhaseFlipChannel
     cirq.ResetChannel
+    cirq.VirtualTag
 
 
 Pauli and Clifford Groups