# 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 cirq.ops import op_tree, 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."""
[docs] def on_each(self, *targets: raw_types.Qid) -> op_tree.OP_TREE:
"""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.
"""
if any([not isinstance(target, raw_types.Qid)
for target in targets]):
raise ValueError(
'on_each() was called with type different than Qid.')
return [self.on(target) for target in targets]
[docs]class TwoQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to exactly two qubits."""
[docs]class ThreeQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to exactly three qubits."""
class MultiQubitGate(raw_types.Gate, metaclass=abc.ABCMeta):
"""A gate that must be applied to multiple qubits.
This class can be used to get rid of a bit of boiler plate. Typically one
would implement a multiqubit gate like
class MyGate:
def __init__(self, num_qubits, **args):
self._num_qubits
# other arg work
def num_qubits(self):
return self._num_qubits
def validate_args(self, qubits):
if self.num_qubits != len(qubits):
raise ValueError('Acting on wrong number of qubits')
This class allows you to instead use
class MyGate(MultiQubitGate):
def __init__(self, num_qubits, **args):
super().__init__(num_qubits)
# other arg work
Validation of number of qubits is handled in this class. If more validation
is necessary, remember to call the super method:
def validate_args(self, qubits):
super().validate_args(qubits)
# your validation here
"""
def __init__(self, num_qubits: int):
self._num_qubits = num_qubits
def num_qubits(self) -> int:
return self._num_qubits
def validate_args(self, qubits):
if len(qubits) != self.num_qubits():
raise ValueError(
'{}-qubit gate was applied to {} qubits'.
format(self.num_qubits(), len(qubits)))
```