Remove unnecessary casts and type: ignores (quantumlib#5781)

Update mypy configuration to fail if there are unnecessary `cast` calls or `type: ignore` comments, so that we clean these up rather than accumulating cruft.

cirq-aqt/cirq_aqt/aqt_device_test.py

@@ -24,7 +24,7 @@
 
 def aqt_device(chain_length: int, use_timedelta=False) -> cad.AQTDevice:
     ms = 1000 * cirq.Duration(nanos=1) if not use_timedelta else timedelta(microseconds=1)
-    return cad.AQTDevice(  # type: ignore
+    return cad.AQTDevice(
         measurement_duration=100 * ms,  # type: ignore
         twoq_gates_duration=200 * ms,  # type: ignore
         oneq_gates_duration=10 * ms,  # type: ignore

cirq-core/cirq/_compat_test.py

@@ -367,7 +367,7 @@ class BadlyDeprecatedClass(NewClass):
 
 
 def _from_parent_import_deprecated():
-    from cirq.testing._compat_test_data import fake_a  # type: ignore
+    from cirq.testing._compat_test_data import fake_a
 
     assert fake_a.MODULE_A_ATTRIBUTE == 'module_a'
 
@@ -379,7 +379,7 @@ def _import_deprecated_assert_sub():
 
 
 def _from_deprecated_import_sub():
-    from cirq.testing._compat_test_data.fake_a import module_b  # type: ignore
+    from cirq.testing._compat_test_data.fake_a import module_b
 
     assert module_b.MODULE_B_ATTRIBUTE == 'module_b'
 
@@ -450,7 +450,7 @@ def _import_multiple_deprecated():
     from cirq.testing._compat_test_data.module_a.module_b import module_c
 
     assert module_c.MODULE_C_ATTRIBUTE == 'module_c'
-    from cirq.testing._compat_test_data.fake_a.module_b import module_c  # type: ignore
+    from cirq.testing._compat_test_data.fake_a.module_b import module_c
 
     assert module_c.MODULE_C_ATTRIBUTE == 'module_c'
     from cirq.testing._compat_test_data.fake_b import module_c  # type: ignore
@@ -531,7 +531,7 @@ def _repeated_import_path():
 
     # pylint: disable=line-too-long
     from cirq.testing._compat_test_data.repeated_child.cirq.testing._compat_test_data.repeated_child import (  # type: ignore
-        child,  # type: ignore
+        child,
     )
 
     assert child.CHILD_ATTRIBUTE == 'child'
@@ -798,7 +798,7 @@ def _test_broken_module_2_inner():
             match="missing_module cannot be imported. The typical reasons",
         ):
             # note that this passes
-            from cirq.testing._compat_test_data import broken_ref  # type: ignore
+            from cirq.testing._compat_test_data import broken_ref
 
             # but when you try to use it
             broken_ref.something()

cirq-core/cirq/circuits/circuit.py

@@ -2073,7 +2073,7 @@ def insert(
                 self._moments.insert(k, moment_or_op)
                 k += 1
             else:
-                op = cast(ops.Operation, moment_or_op)
+                op = moment_or_op
                 p = self._pick_or_create_inserted_op_moment_index(k, op, strategy)
                 while p >= len(self._moments):
                     self._moments.append(Moment())

cirq-core/cirq/contrib/qcircuit/qcircuit_diagram_info.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import cast, Optional, Tuple
+from typing import Optional, Tuple
 
 from cirq import ops, protocols
 
@@ -59,7 +59,7 @@ def hardcoded_qcircuit_diagram_info(op: ops.Operation) -> Optional[protocols.Cir
         if isinstance(op.gate, ops.MeasurementGate)
         else ()
     )
-    return protocols.CircuitDiagramInfo(cast(Tuple[str, ...], symbols)) if symbols else None
+    return protocols.CircuitDiagramInfo(symbols) if symbols else None
 
 
 def convert_text_diagram_info_to_qcircuit_diagram_info(

cirq-core/cirq/contrib/quantum_volume/quantum_volume.py

@@ -4,7 +4,7 @@
 """
 
 from dataclasses import dataclass
-from typing import Optional, List, cast, Callable, Dict, Tuple, Set, Any
+from typing import Optional, List, Callable, Dict, Tuple, Set, Any
 
 import networkx as nx
 import numpy as np
@@ -75,7 +75,7 @@ def compute_heavy_set(circuit: cirq.Circuit) -> List[int]:
     # Classically compute the probabilities of each output bit-string through
     # simulation.
     simulator = cirq.Simulator()
-    results = cast(cirq.StateVectorTrialResult, simulator.simulate(program=circuit))
+    results = simulator.simulate(program=circuit)
 
     # Compute the median probability of the output bit-strings. Note that heavy
     # output is defined in terms of probabilities, where our wave function is in

cirq-core/cirq/contrib/svg/svg.py

@@ -216,7 +216,6 @@ def tdd_to_svg(
         t += f'<line x1="{x}" x2="{x}" y1="{y1}" y2="{y2}" stroke="black" stroke-width="3" />'
 
     for (xi, yi), v in tdd.entries.items():
-        xi = cast(int, xi)
         yi = yi_map[yi]
 
         x = col_starts[xi] + col_widths[xi] / 2

cirq-core/cirq/devices/grid_qubit.py

@@ -24,7 +24,7 @@
 if TYPE_CHECKING:
     import cirq
 
-TSelf = TypeVar('TSelf', bound='_BaseGridQid')  # type: ignore
+TSelf = TypeVar('TSelf', bound='_BaseGridQid')
 
 
 @functools.total_ordering  # type: ignore

cirq-core/cirq/devices/line_qubit.py

@@ -22,7 +22,7 @@
 if TYPE_CHECKING:
     import cirq
 
-TSelf = TypeVar('TSelf', bound='_BaseLineQid')  # type: ignore
+TSelf = TypeVar('TSelf', bound='_BaseLineQid')
 
 
 @functools.total_ordering  # type: ignore

cirq-core/cirq/devices/noise_model.py

@@ -283,7 +283,7 @@ def noisy_moment(
 
 NOISE_MODEL_LIKE = Union[None, 'cirq.NoiseModel', 'cirq.Gate']
 document(
-    NOISE_MODEL_LIKE,  # type: ignore
+    NOISE_MODEL_LIKE,
     """A `cirq.NoiseModel` or a value that can be trivially converted into one.
 
     `None` is a `NOISE_MODEL_LIKE`. It will be replaced by the `cirq.NO_NOISE`

cirq-core/cirq/interop/quirk/cells/parse.py

@@ -154,7 +154,7 @@ def apply(op: Union[str, _HangingNode]) -> None:
         a = vals.pop()
         # Note: vals seems to be _HangingToken
         # func operates on _ResolvedTokens. Ignoring type issues for now.
-        vals.append(cast(_HangingNode, op).func(a, b))  # type: ignore[arg-type]
+        vals.append(op.func(a, b))  # type: ignore[arg-type]
 
     def close_paren() -> None:
         while True:
@@ -176,10 +176,7 @@ def feed_op(could_be_binary: bool, token: Any) -> None:
         # Implied multiplication?
         mul = cast(_CustomQuirkOperationToken, token_map["*"])
         if could_be_binary and token != ")":
-            if (
-                not isinstance(token, _CustomQuirkOperationToken)
-                or cast(_CustomQuirkOperationToken, token).binary_action is None
-            ):
+            if not isinstance(token, _CustomQuirkOperationToken) or token.binary_action is None:
                 burn_ops(mul.priority)
                 ops.append(
                     _HangingNode(

cirq-core/cirq/interop/quirk/url_to_circuit.py

@@ -235,7 +235,7 @@ def msg(error):
 
     # Remap qubits if requested.
     if qubits is not None:
-        qs = cast(Sequence['cirq.Qid'], qubits)
+        qs = qubits
 
         def map_qubit(qubit: 'cirq.Qid') -> 'cirq.Qid':
             q = cast(devices.LineQubit, qubit)

cirq-core/cirq/json_resolver_cache.py

@@ -232,13 +232,13 @@ def _symmetricalqidpair(qids):
         # pylint: disable=line-too-long
         'XEBPhasedFSimCharacterizationOptions': cirq.experiments.XEBPhasedFSimCharacterizationOptions,
         # pylint: enable=line-too-long
-        '_XEigenState': cirq.value.product_state._XEigenState,  # type: ignore
+        '_XEigenState': cirq.value.product_state._XEigenState,
         'XPowGate': cirq.XPowGate,
         'XXPowGate': cirq.XXPowGate,
-        '_YEigenState': cirq.value.product_state._YEigenState,  # type: ignore
+        '_YEigenState': cirq.value.product_state._YEigenState,
         'YPowGate': cirq.YPowGate,
         'YYPowGate': cirq.YYPowGate,
-        '_ZEigenState': cirq.value.product_state._ZEigenState,  # type: ignore
+        '_ZEigenState': cirq.value.product_state._ZEigenState,
         'Zip': cirq.Zip,
         'ZPowGate': cirq.ZPowGate,
         'ZZPowGate': cirq.ZZPowGate,

cirq-core/cirq/ops/classically_controlled_operation.py

@@ -15,7 +15,6 @@
     AbstractSet,
     Any,
     Mapping,
-    cast,
     Dict,
     FrozenSet,
     List,
@@ -85,7 +84,7 @@ def __init__(
                 c = value.KeyCondition(c)
             if isinstance(c, sympy.Basic):
                 c = value.SympyCondition(c)
-            conds.append(cast('cirq.Condition', c))
+            conds.append(c)
         self._conditions: Tuple['cirq.Condition', ...] = tuple(conds)
         self._sub_operation: 'cirq.Operation' = sub_operation
 

cirq-core/cirq/ops/clifford_gate.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Any, cast, Dict, List, Optional, Sequence, Tuple, TYPE_CHECKING, Union
+from typing import Any, Dict, List, Optional, Sequence, Tuple, TYPE_CHECKING, Union
 
 
 import numpy as np
@@ -90,7 +90,7 @@ def _validate_map_input(
 ) -> Dict[Pauli, Tuple[Pauli, bool]]:
     if pauli_map_to is None:
         xyz_to = {pauli_gates.X: x_to, pauli_gates.Y: y_to, pauli_gates.Z: z_to}
-        pauli_map_to = {cast(Pauli, p): trans for p, trans in xyz_to.items() if trans is not None}
+        pauli_map_to = {p: trans for p, trans in xyz_to.items() if trans is not None}
     elif x_to is not None or y_to is not None or z_to is not None:
         raise ValueError(
             '{} can take either pauli_map_to or a combination'
@@ -531,9 +531,7 @@ def from_single_map(
             trans_to2 = trans_from
             flip2 = not flip
         rotation_map[trans_from2] = (trans_to2, flip2)
-        return SingleQubitCliffordGate.from_double_map(
-            cast(Dict[Pauli, Tuple[Pauli, bool]], rotation_map)
-        )
+        return SingleQubitCliffordGate.from_double_map(rotation_map)
 
     @staticmethod
     def from_double_map(

cirq-core/cirq/ops/common_gate_families.py

@@ -148,7 +148,7 @@ def __init__(
         if isinstance(gate, parallel_gate.ParallelGate):
             if not max_parallel_allowed:
                 max_parallel_allowed = protocols.num_qubits(gate)
-            gate = cast(parallel_gate.ParallelGate, gate).sub_gate
+            gate = gate.sub_gate
         self._max_parallel_allowed = max_parallel_allowed
         super().__init__(gate, name=name, description=description)
 

cirq-core/cirq/ops/control_values.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import abc
-from typing import Union, Tuple, List, TYPE_CHECKING, Any, Dict, Generator, cast, Iterator, Optional
+from typing import Union, Tuple, List, TYPE_CHECKING, Any, Dict, Generator, Iterator, Optional
 from dataclasses import dataclass
 
 import itertools
@@ -121,7 +121,6 @@ def _identifier(self) -> Tuple[Tuple[int, ...], ...]:
 
     def _expand(self) -> Iterator[Tuple[int, ...]]:
         """Returns the combinations tracked by the object."""
-        self = cast('ProductOfSums', self)
         return itertools.product(*self._internal_representation)
 
     def __repr__(self) -> str:
@@ -231,7 +230,6 @@ def _identifier(self) -> Tuple[Tuple[int, ...], ...]:
 
     def _expand(self) -> Iterator[Tuple[int, ...]]:
         """Returns the combinations tracked by the object."""
-        self = cast('SumOfProducts', self)
         return iter(self._internal_representation)
 
     def __repr__(self) -> str:

cirq-core/cirq/ops/controlled_gate.py

@@ -112,7 +112,7 @@ def __init__(
 
         # Flatten nested ControlledGates.
         if isinstance(sub_gate, ControlledGate):
-            self._sub_gate = sub_gate.sub_gate  # type: ignore
+            self._sub_gate = sub_gate.sub_gate
             self._control_values = self._control_values & sub_gate.control_values
             self._control_qid_shape += sub_gate.control_qid_shape
         else:

cirq-core/cirq/ops/linear_combinations.py

@@ -50,7 +50,7 @@
     int, float, complex, PauliString, 'PauliSum', pauli_string.SingleQubitPauliStringGateOperation
 ]
 document(
-    PauliSumLike,  # type: ignore
+    PauliSumLike,
     """Any value that can be easily translated into a sum of Pauli products.
     """,
 )

cirq-core/cirq/ops/matrix_gates.py

@@ -14,7 +14,7 @@
 
 """Quantum gates defined by a matrix."""
 
-from typing import Any, cast, Dict, Iterable, Optional, Tuple, TYPE_CHECKING
+from typing import Any, Dict, Iterable, Optional, Tuple, TYPE_CHECKING
 
 import numpy as np
 
@@ -115,8 +115,7 @@ def _qid_shape_(self) -> Tuple[int, ...]:
     def __pow__(self, exponent: Any) -> 'MatrixGate':
         if not isinstance(exponent, (int, float)):
             return NotImplemented
-        e = cast(float, exponent)
-        new_mat = linalg.map_eigenvalues(self._matrix, lambda b: b**e)
+        new_mat = linalg.map_eigenvalues(self._matrix, lambda b: b**exponent)
         return MatrixGate(new_mat, qid_shape=self._qid_shape)
 
     def _phase_by_(self, phase_turns: float, qubit_index: int) -> 'MatrixGate':

cirq-core/cirq/ops/named_qubit.py

@@ -21,7 +21,7 @@
 if TYPE_CHECKING:
     import cirq
 
-TSelf = TypeVar('TSelf', bound='_BaseNamedQid')  # type: ignore
+TSelf = TypeVar('TSelf', bound='_BaseNamedQid')
 
 
 @functools.total_ordering  # type: ignore

cirq-core/cirq/ops/op_tree.py

@@ -55,7 +55,7 @@ def __iter__(self) -> Iterator[Union[Operation, 'OpTree']]:
 
 OP_TREE = Union[Operation, OpTree]
 document(
-    OP_TREE,  # type: ignore
+    OP_TREE,
     """An operation or nested collections of operations.
 
     Here are some examples of things that can be given to a method that takes a

cirq-core/cirq/ops/pauli_string.py

@@ -78,7 +78,7 @@
     Iterable,  # of PAULI_STRING_LIKE, but mypy doesn't do recursive types yet.
 ]
 document(
-    PAULI_STRING_LIKE,  # type: ignore
+    PAULI_STRING_LIKE,
     """A `cirq.PauliString` or a value that can easily be converted into one.
 
     Complex numbers turn into the coefficient of an empty Pauli string.
@@ -94,7 +94,7 @@
 
 PAULI_GATE_LIKE = Union['cirq.Pauli', 'cirq.IdentityGate', str, int,]
 document(
-    PAULI_GATE_LIKE,  # type: ignore
+    PAULI_GATE_LIKE,
     """An object that can be interpreted as a Pauli gate.
 
     Allowed values are:
@@ -1715,4 +1715,4 @@ def _pauli_like_to_pauli_int(key: Any, pauli_gate_like: PAULI_GATE_LIKE):
             f"But the value isn't in "
             f"{set(PAULI_GATE_LIKE_TO_INDEX_MAP.keys())!r}"
         )
-    return cast(int, pauli_int)
+    return pauli_int

cirq-core/cirq/ops/pauli_string_test.py

@@ -14,7 +14,7 @@
 
 import itertools
 import math
-from typing import List, cast
+from typing import List
 
 import numpy as np
 import pytest
@@ -656,10 +656,7 @@ def _assert_pass_over(ops: List[cirq.Operation], before: cirq.PauliString, after
 @pytest.mark.parametrize('shift,sign', itertools.product(range(3), (-1, +1)))
 def test_pass_operations_over_single(shift: int, sign: int):
     q0, q1 = _make_qubits(2)
-    X, Y, Z = (
-        cirq.Pauli.by_relative_index(cast(cirq.Pauli, pauli), shift)
-        for pauli in (cirq.X, cirq.Y, cirq.Z)
-    )
+    X, Y, Z = (cirq.Pauli.by_relative_index(pauli, shift) for pauli in (cirq.X, cirq.Y, cirq.Z))
 
     op0 = cirq.SingleQubitCliffordGate.from_pauli(Y)(q1)
     ps_before: cirq.PauliString[cirq.Qid] = cirq.PauliString({q0: X}, sign)
@@ -698,10 +695,7 @@ def test_pass_operations_over_single(shift: int, sign: int):
 def test_pass_operations_over_double(shift: int, t_or_f1: bool, t_or_f2: bool, neg: bool):
     sign = -1 if neg else +1
     q0, q1, q2 = _make_qubits(3)
-    X, Y, Z = (
-        cirq.Pauli.by_relative_index(cast(cirq.Pauli, pauli), shift)
-        for pauli in (cirq.X, cirq.Y, cirq.Z)
-    )
+    X, Y, Z = (cirq.Pauli.by_relative_index(pauli, shift) for pauli in (cirq.X, cirq.Y, cirq.Z))
 
     op0 = cirq.PauliInteractionGate(Z, t_or_f1, X, t_or_f2)(q0, q1)
     ps_before = cirq.PauliString(qubit_pauli_map={q0: Z, q2: Y}, coefficient=sign)

cirq-core/cirq/ops/qubit_order_or_list.py

@@ -25,7 +25,7 @@
 
 QubitOrderOrList = Union[qubit_order.QubitOrder, Iterable[raw_types.Qid]]
 document(
-    QubitOrderOrList,  # type: ignore
+    QubitOrderOrList,
     """Specifies a qubit ordering.
 
     The ordering can either be specified by an iterable (such as a list) with

cirq-core/cirq/protocols/json_serialization.py

@@ -729,7 +729,7 @@ def to_json_gzip(
             actually_a_file.write(json_str)
             return None
 
-    gzip_data = gzip.compress(bytes(json_str, encoding='utf-8'))  # type: ignore
+    gzip_data = gzip.compress(bytes(json_str, encoding='utf-8'))
     if file_or_fn is None:
         return gzip_data
 

cirq-core/cirq/protocols/json_serialization_test.py

@@ -79,7 +79,7 @@ def _get_testspecs_for_modules() -> List[ModuleJsonTestSpec]:
 def test_deprecated_cirq_type_in_json_dict():
     class HasOldJsonDict:
         # Required for testing serialization of non-cirq objects.
-        __module__ = 'test.noncirq.namespace'  # type: ignore
+        __module__ = 'test.noncirq.namespace'
 
         def __eq__(self, other):
             return isinstance(other, HasOldJsonDict)