Make _commutes_ consistent (quantumlib#5217)

- Requires atol to be a named parameter.
- Also changes atol to be uniformly float around the codebase.
  (not sure why it would be int, are people using an atol=1?)
- Technically a breaking change, but it's unlikely people are using
  this widely as most commutes do not even use atol.

Fixes: quantumlib#3695

cirq-core/cirq/circuits/moment.py

@@ -574,9 +574,7 @@ def cleanup_key(key: Any) -> Any:
 
         return diagram.render()
 
-    def _commutes_(
-        self, other: Any, *, atol: Union[int, float] = 1e-8
-    ) -> Union[bool, NotImplementedType]:
+    def _commutes_(self, other: Any, *, atol: float = 1e-8) -> Union[bool, NotImplementedType]:
         """Determines whether Moment commutes with the Operation.
 
         Args:

cirq-core/cirq/contrib/acquaintance/permutation.py

@@ -164,9 +164,7 @@ def __repr__(self) -> str:
     def _value_equality_values_(self) -> Any:
         return (self.swap_gate,)
 
-    def _commutes_(
-        self, other: Any, atol: Union[int, float] = 1e-8
-    ) -> Union[bool, NotImplementedType]:
+    def _commutes_(self, other: Any, *, atol: float = 1e-8) -> Union[bool, NotImplementedType]:
         if (
             isinstance(other, ops.Gate)
             and isinstance(other, ops.InterchangeableQubitsGate)

cirq-core/cirq/ops/clifford_gate.py

@@ -383,7 +383,7 @@ def __pow__(self, exponent) -> 'SingleQubitCliffordGate':
 
         return SingleQubitCliffordGate.from_clifford_tableau(self.clifford_tableau.inverse())
 
-    def _commutes_(self, other: Any, atol: float) -> Union[bool, NotImplementedType]:
+    def _commutes_(self, other: Any, *, atol: float = 1e-8) -> Union[bool, NotImplementedType]:
         if isinstance(other, SingleQubitCliffordGate):
             return self.commutes_with_single_qubit_gate(other)
         if isinstance(other, Pauli):
@@ -838,7 +838,9 @@ def __pow__(self, exponent) -> 'CliffordGate':
     def __repr__(self) -> str:
         return f"Clifford Gate with Tableau:\n {self.clifford_tableau._str_full_()}"
 
-    def _commutes_(self, other: Any, atol: float) -> Union[bool, NotImplementedType, None]:
+    def _commutes_(
+        self, other: Any, *, atol: float = 1e-8
+    ) -> Union[bool, NotImplementedType, None]:
         # Note even if we assume two gates define the tabluea based on the same qubit order,
         # the following approach cannot judge it:
         # self.clifford_tableau.then(other.clifford_tableau) == other.clifford_tableau.then(

cirq-core/cirq/ops/common_gates.py

@@ -662,7 +662,7 @@ def __repr__(self) -> str:
         )
 
     def _commutes_on_qids_(
-        self, qids: 'Sequence[cirq.Qid]', other: Any, atol: float
+        self, qids: 'Sequence[cirq.Qid]', other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         from cirq.ops.parity_gates import ZZPowGate
 

cirq-core/cirq/ops/dense_pauli_string.py

@@ -358,7 +358,9 @@ def __repr__(self) -> str:
             f'coefficient={proper_repr(self.coefficient)})'
         )
 
-    def _commutes_(self, other: Any, atol: float) -> Union[bool, NotImplementedType, None]:
+    def _commutes_(
+        self, other: Any, *, atol: float = 1e-8
+    ) -> Union[bool, NotImplementedType, None]:
         if isinstance(other, BaseDensePauliString):
             n = min(len(self.pauli_mask), len(other.pauli_mask))
             phase = _vectorized_pauli_mul_phase(self.pauli_mask[:n], other.pauli_mask[:n])

cirq-core/cirq/ops/gate_operation.py

@@ -199,7 +199,7 @@ def _unitary_(self) -> Union[np.ndarray, NotImplementedType]:
         return NotImplemented
 
     def _commutes_(
-        self, other: Any, atol: Union[int, float] = 1e-8
+        self, other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         commutes = self.gate._commutes_on_qids_(self.qubits, other, atol=atol)
         if commutes is not NotImplemented:

cirq-core/cirq/ops/pauli_gates.py

@@ -53,7 +53,9 @@ def __init__(self, index: int, name: str) -> None:
     def num_qubits(self):
         return 1
 
-    def _commutes_(self, other: Any, atol: float) -> Union[bool, NotImplementedType, None]:
+    def _commutes_(
+        self, other: Any, *, atol: float = 1e-8
+    ) -> Union[bool, NotImplementedType, None]:
         if not isinstance(other, Pauli):
             return NotImplemented
         return self is other

cirq-core/cirq/ops/pauli_string.py

@@ -678,7 +678,7 @@ def zip_paulis(
         return (paulis for qubit, paulis in self.zip_items(other))
 
     def _commutes_(
-        self, other: Any, *, atol: Union[int, float] = 1e-8
+        self, other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         if not isinstance(other, PauliString):
             return NotImplemented

cirq-core/cirq/ops/raw_types.py

@@ -399,11 +399,13 @@ def _qid_shape_(self) -> Tuple[int, ...]:
         """
 
     def _commutes_on_qids_(
-        self, qids: 'Sequence[cirq.Qid]', other: Any, atol: float
+        self, qids: 'Sequence[cirq.Qid]', other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         return NotImplemented
 
-    def _commutes_(self, other: Any, atol: float) -> Union[None, NotImplementedType, bool]:
+    def _commutes_(
+        self, other: Any, *, atol: float = 1e-8
+    ) -> Union[None, NotImplementedType, bool]:
         if not isinstance(other, Gate):
             return NotImplemented
         if protocols.qid_shape(self) != protocols.qid_shape(other):
@@ -567,7 +569,7 @@ def validate_args(self, qubits: Sequence['cirq.Qid']):
         _validate_qid_shape(self, qubits)
 
     def _commutes_(
-        self, other: Any, *, atol: Union[int, float] = 1e-8
+        self, other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         """Determine if this Operation commutes with the object"""
         if not isinstance(other, Operation):
@@ -771,7 +773,7 @@ def _unitary_(self) -> Union[np.ndarray, NotImplementedType]:
         return protocols.unitary(self.sub_operation, NotImplemented)
 
     def _commutes_(
-        self, other: Any, *, atol: Union[int, float] = 1e-8
+        self, other: Any, *, atol: float = 1e-8
     ) -> Union[bool, NotImplementedType, None]:
         return protocols.commutes(self.sub_operation, other, atol=atol)
 

cirq-core/cirq/protocols/commutes_protocol.py

@@ -35,7 +35,7 @@ class SupportsCommutes(Protocol):
     """An object that can determine commutation relationships vs others."""
 
     @doc_private
-    def _commutes_(self, other: Any, atol: float) -> Union[None, bool, NotImplementedType]:
+    def _commutes_(self, other: Any, *, atol: float) -> Union[None, bool, NotImplementedType]:
         r"""Determines if this object commutes with the other object.
 
         Can return None to indicate the commutation relationship is