Remove public fields for pauli ops (quantumlib#5062)

quantumlib#4851 for all the pauli stuff.

I skipped BaseDensePauliString because including `cirq._compat` there makes a weird circular dependency.

cirq/ops/pauli_interaction_gate.py

@@ -17,7 +17,7 @@
 import numpy as np
 
 from cirq import value, protocols
-from cirq._compat import proper_repr
+from cirq._compat import deprecated, proper_repr
 from cirq.ops import gate_features, common_gates, eigen_gate, pauli_gates
 from cirq.ops.clifford_gate import SingleQubitCliffordGate
 
@@ -66,10 +66,58 @@ def __init__(
                 equal to the tensor product of the two conditions.
         """
         super().__init__(exponent=exponent)
-        self.pauli0 = pauli0
-        self.invert0 = invert0
-        self.pauli1 = pauli1
-        self.invert1 = invert1
+        self._pauli0 = pauli0
+        self._invert0 = invert0
+        self._pauli1 = pauli1
+        self._invert1 = invert1
+
+    @property
+    def pauli0(self) -> 'cirq.Pauli':
+        return self._pauli0
+
+    @pauli0.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def pauli0(self, pauli0: 'cirq.Pauli'):
+        self._pauli0 = pauli0
+
+    @property
+    def invert0(self) -> bool:
+        return self._invert0
+
+    @invert0.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def invert0(self, invert0: bool):
+        self._invert0 = invert0
+
+    @property
+    def pauli1(self) -> 'cirq.Pauli':
+        return self._pauli1
+
+    @pauli1.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def pauli1(self, pauli1: 'cirq.Pauli'):
+        self._pauli1 = pauli1
+
+    @property
+    def invert1(self) -> bool:
+        return self._invert1
+
+    @invert1.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def invert1(self, invert1: bool):
+        self._invert1 = invert1
 
     def _num_qubits_(self) -> int:
         return 2

cirq/ops/pauli_interaction_gate_test.py

@@ -126,3 +126,19 @@ def test_text_diagrams():
 q1: ───X───X──────(-X)───(-X)───Y───@───Y───(-@)───(-Y)───
     """.strip()
     )
+
+
+def test_setters_deprecated():
+    gate = cirq.PauliInteractionGate(cirq.X, False, cirq.X, False)
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.pauli0 = cirq.Y
+    assert gate.pauli0 == cirq.Y
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.pauli1 = cirq.Y
+    assert gate.pauli1 == cirq.Y
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.invert0 = True
+    assert gate.invert0
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.invert1 = True
+    assert gate.invert1

cirq/ops/pauli_measurement_gate.py

@@ -15,6 +15,7 @@
 from typing import Any, Dict, FrozenSet, Iterable, Tuple, Sequence, TYPE_CHECKING, Union, cast
 
 from cirq import protocols, value
+from cirq._compat import deprecated
 from cirq.ops import (
     raw_types,
     measurement_gate,
@@ -68,17 +69,35 @@ def __init__(
             )
 
         self._observable = dps.DensePauliString(observable, coefficient=coefficient)
-        self.key = key  # type: ignore
+        self._mkey = (
+            key if isinstance(key, value.MeasurementKey) else value.MeasurementKey(name=key)
+        )
 
     @property
     def key(self) -> str:
         return str(self.mkey)
 
-    @key.setter
-    def key(self, key: Union[str, 'cirq.MeasurementKey']) -> None:
+    @key.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def key(self, key: Union[str, 'cirq.MeasurementKey']):
         if isinstance(key, str):
             key = value.MeasurementKey(name=key)
-        self.mkey = key
+        self._mkey = key
+
+    @property
+    def mkey(self) -> 'cirq.MeasurementKey':
+        return self._mkey
+
+    @mkey.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def mkey(self, mkey: 'cirq.MeasurementKey'):
+        self._mkey = mkey
 
     def _qid_shape_(self) -> Tuple[int, ...]:
         return (2,) * len(self._observable)

cirq/ops/pauli_measurement_gate_test.py

@@ -195,3 +195,19 @@ def test_pauli_measurement_gate_samples(rot, obs, out):
     q = cirq.NamedQubit("q")
     c = cirq.Circuit(rot(q), cirq.PauliMeasurementGate(obs, key='out').on(q))
     assert cirq.Simulator().sample(c)['out'][0] == out
+
+
+def test_setters_deprecated():
+    gate = cirq.PauliMeasurementGate(cirq.DensePauliString("Z", coefficient=+1), key='m')
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.key = 'n'
+    assert gate.key == 'n'
+    assert gate.mkey == cirq.MeasurementKey('n')
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.key = cirq.MeasurementKey('o')
+    assert gate.key == 'o'
+    assert gate.mkey == cirq.MeasurementKey('o')
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.mkey = cirq.MeasurementKey('p')
+    assert gate.key == 'p'
+    assert gate.mkey == cirq.MeasurementKey('p')

cirq/ops/pauli_string_raw_types.py

@@ -17,6 +17,7 @@
 import abc
 
 from cirq import protocols
+from cirq._compat import deprecated
 from cirq.ops import pauli_string as ps, raw_types
 
 if TYPE_CHECKING:
@@ -29,7 +30,19 @@
 
 class PauliStringGateOperation(raw_types.Operation, metaclass=abc.ABCMeta):
     def __init__(self, pauli_string: ps.PauliString) -> None:
-        self.pauli_string = pauli_string
+        self._pauli_string = pauli_string
+
+    @property
+    def pauli_string(self) -> 'cirq.PauliString':
+        return self._pauli_string
+
+    @pauli_string.setter  # type: ignore
+    @deprecated(
+        deadline="v0.15",
+        fix="The mutators of this class are deprecated, instantiate a new object instead.",
+    )
+    def pauli_string(self, pauli_string: 'cirq.PauliString'):
+        self._pauli_string = pauli_string
 
     def validate_args(self, qubits: Sequence[raw_types.Qid]) -> None:
         if len(qubits) != len(self.pauli_string):

cirq/ops/pauli_string_raw_types_test.py

@@ -91,3 +91,16 @@ def _circuit_diagram_info_(
 q2: ───[Z]───[Z]───
 """,
     )
+
+
+def test_setters_deprecated():
+    q0 = cirq.LineQubit(0)
+
+    class DummyGate(cirq.PauliStringGateOperation):
+        def map_qubits(self, qubit_map):
+            pass
+
+    gate = DummyGate(cirq.PauliString({q0: cirq.X}))
+    with cirq.testing.assert_deprecated('mutators', deadline='v0.15'):
+        gate.pauli_string = cirq.PauliString({q0: cirq.Z})
+    assert gate.pauli_string == cirq.PauliString({q0: cirq.Z})