/
act_on_protocol.py
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/
act_on_protocol.py
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# Copyright 2020 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.
from typing import Any, Sequence, TYPE_CHECKING, Union
from typing_extensions import Protocol
from cirq import _compat, ops
from cirq._doc import doc_private
from cirq.type_workarounds import NotImplementedType
if TYPE_CHECKING:
import cirq
class SupportsActOn(Protocol):
"""An object that explicitly specifies how to act on simulator states."""
@doc_private
def _act_on_(self, sim_state: 'cirq.SimulationStateBase') -> Union[NotImplementedType, bool]:
"""Applies an action to the given argument, if it is a supported type.
For example, unitary operations can implement an `_act_on_` method that
checks if `isinstance(sim_state, cirq.StateVectorSimulationState)` and,
if so, apply their unitary effect to the state vector.
The global `cirq.act_on` method looks for whether or not the given
argument has this value, before attempting any fallback strategies
specified by the argument being acted on.
This should only be implemented on `Operation` subclasses. Others such
as gates should use `SupportsActOnQubits`.
Args:
sim_state: An object of unspecified type. The method must check if
this object is of a recognized type and act on it if so.
Returns:
True: The receiving object (`self`) acted on the argument.
NotImplemented: The receiving object did not act on the argument.
All other return values are considered to be errors.
"""
class SupportsActOnQubits(Protocol):
"""An object that explicitly specifies how to act on specific qubits."""
@doc_private
def _act_on_(
self, sim_state: 'cirq.SimulationStateBase', qubits: Sequence['cirq.Qid']
) -> Union[NotImplementedType, bool]:
"""Applies an action to the given argument, if it is a supported type.
For example, unitary operations can implement an `_act_on_` method that
checks if `isinstance(sim_state, cirq.StateVectorSimulationState)` and,
if so, apply their unitary effect to the state vector.
The global `cirq.act_on` method looks for whether or not the given
argument has this value, before attempting any fallback strategies
specified by the argument being acted on.
If implementing this on an `Operation`, use `SupportsActOn` instead.
Args:
sim_state: An object of unspecified type. The method must check if
this object is of a recognized type and act on it if so.
qubits: The sequence of qubits to use when applying the action.
Returns:
True: The receiving object (`self`) acted on the argument.
NotImplemented: The receiving object did not act on the argument.
All other return values are considered to be errors.
"""
def _fix_deprecated_args(args, kwargs):
kwargs['sim_state'] = kwargs['args']
del kwargs['args']
return args, kwargs
@_compat.deprecated_parameter(
deadline='v0.16',
fix='Change argument name to `sim_state`',
parameter_desc='args',
match=lambda args, kwargs: 'args' in kwargs,
rewrite=_fix_deprecated_args,
)
def act_on(
action: Any,
sim_state: 'cirq.SimulationStateBase',
qubits: Sequence['cirq.Qid'] = None,
*,
allow_decompose: bool = True,
):
"""Applies an action to a state argument.
For example, the action may be a `cirq.Operation` and the state argument may
represent the internal state of a state vector simulator (a
`cirq.StateVectorSimulationState`).
For non-operations, the `qubits` argument must be explicitly supplied.
The action is applied by first checking if `action._act_on_` exists and
returns `True` (instead of `NotImplemented`) for the given object. Then
fallback strategies specified by the state argument via `_act_on_fallback_`
are attempted. If those also fail, the method fails with a `TypeError`.
Args:
action: The operation, gate, or other to apply to the state tensor.
sim_state: A mutable state object that should be modified by the
action. May specify an `_act_on_fallback_` method to use in case
the action doesn't recognize it.
qubits: The sequence of qubits to use when applying the action.
allow_decompose: Defaults to True. Forwarded into the
`_act_on_fallback_` method of `sim_state`. Determines if
decomposition should be used or avoided when attempting to act
`action` on `sim_state`. Used by internal methods to avoid
redundant decompositions.
Returns:
Nothing. Results are communicated by editing `sim_state`.
Raises:
ValueError: If called on an operation and supplied qubits, if not called
on an operation and no qubits are supplied, or if `_act_on_` or
`_act_on_fallback_` returned something other than `True` or
`NotImplemented`.
TypeError: Failed to act `action` on `sim_state`.
"""
is_op = isinstance(action, ops.Operation)
if is_op and qubits is not None:
raise ValueError('Calls to act_on should not supply qubits if the action is an Operation.')
if not is_op and qubits is None:
raise ValueError('Calls to act_on should supply qubits if the action is not an Operation.')
action_act_on = getattr(action, '_act_on_', None)
if action_act_on is not None:
result = action_act_on(sim_state) if is_op else action_act_on(sim_state, qubits)
if result is True:
return
if result is not NotImplemented:
raise ValueError(
f'_act_on_ must return True or NotImplemented but got '
f'{result!r} from {action!r}._act_on_'
)
arg_fallback = getattr(sim_state, '_act_on_fallback_', None)
if arg_fallback is not None:
qubits = action.qubits if isinstance(action, ops.Operation) else qubits
result = arg_fallback(action, qubits=qubits, allow_decompose=allow_decompose)
if result is True:
return
if result is not NotImplemented:
raise ValueError(
f'_act_on_fallback_ must return True or NotImplemented but got '
f'{result!r} from {type(sim_state)}._act_on_fallback_'
)
raise TypeError(
"Failed to act action on state argument.\n"
"Tried both action._act_on_ and sim_state._act_on_fallback_.\n"
"\n"
f"State argument type: {type(sim_state)}\n"
f"Action type: {type(action)}\n"
f"Action repr: {action!r}\n"
)