# Source code for cirq.ops.gate_features

```
# Copyright 2018 The Cirq Developers
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Marker classes for indicating which additional features gates support.
For example: some gates are reversible, some have known matrices, etc.
"""
import abc
from typing import Union, Iterable, Any, List
from cirq.ops import raw_types
[docs]class InterchangeableQubitsGate(metaclass=abc.ABCMeta):
"""Indicates operations should be equal under some qubit permutations."""
[docs] def qubit_index_to_equivalence_group_key(self, index: int) -> int:
"""Returns a key that differs between non-interchangeable qubits."""
return 0
[docs]class SingleQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to exactly one qubit."""
def _num_qubits_(self) -> int:
return 1
[docs] def on_each(self, *targets: Union[raw_types.Qid, Iterable[Any]]
) -> List[raw_types.Operation]:
"""Returns a list of operations apply this gate to each of the targets.
Args:
*targets: The qubits to apply this gate to.
Returns:
Operations applying this gate to the target qubits.
Raises:
ValueError if targets are not instances of Qid or List[Qid].
"""
operations = [] # type: List[raw_types.Operation]
for target in targets:
if isinstance(target, Iterable) and not isinstance(target, str):
operations.extend(self.on_each(*target))
elif isinstance(target, raw_types.Qid):
operations.append(self.on(target))
else:
raise ValueError(
'Gate was called with type different than Qid. Type: {}'.
format(type(target)))
return operations
[docs]class TwoQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to exactly two qubits."""
def _num_qubits_(self) -> int:
return 2
[docs]class ThreeQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to exactly three qubits."""
def _num_qubits_(self) -> int:
return 3
```