C贸digo fuente para qiskit.circuit.controlflow.for_loop

# This code is part of Qiskit.
# (C) Copyright IBM 2021.
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"Circuit operation representing a ``for`` loop."

import warnings
from typing import Iterable, Optional, Union

from qiskit.circuit.parameter import Parameter
from qiskit.circuit.exceptions import CircuitError
from qiskit.circuit.quantumcircuit import QuantumCircuit
from .control_flow import ControlFlowOp

[documentos]class ForLoopOp(ControlFlowOp): """A circuit operation which repeatedly executes a subcircuit (``body``) parameterized by a parameter ``loop_parameter`` through the set of integer values provided in ``indexset``. Parameters: indexset: A collection of integers to loop over. loop_parameter: The placeholder parameterizing ``body`` to which the values from ``indexset`` will be assigned. body: The loop body to be repeatedly executed. label: An optional label for identifying the instruction. **Circuit symbol:** .. parsed-literal:: 鈹屸攢鈹鈹鈹鈹鈹鈹鈹鈹鈹鈹鈹 q_0: 鈹0 鈹 鈹 鈹 q_1: 鈹1 鈹 鈹 for_loop 鈹 q_2: 鈹2 鈹 鈹 鈹 c_0: 鈺0 鈺 鈹斺攢鈹鈹鈹鈹鈹鈹鈹鈹鈹鈹鈹 """ def __init__( self, indexset: Iterable[int], loop_parameter: Union[Parameter, None], body: QuantumCircuit, label: Optional[str] = None, ): num_qubits = body.num_qubits num_clbits = body.num_clbits super().__init__( "for_loop", num_qubits, num_clbits, [indexset, loop_parameter, body], label=label ) @property def params(self): return self._params @params.setter def params(self, parameters): indexset, loop_parameter, body = parameters if not isinstance(loop_parameter, (Parameter, type(None))): raise CircuitError( "ForLoopOp expects a loop_parameter parameter to " "be either of type Parameter or None, but received " f"{type(loop_parameter)}." ) if not isinstance(body, QuantumCircuit): raise CircuitError( "ForLoopOp expects a body parameter to be of type " f"QuantumCircuit, but received {type(body)}." ) if body.num_qubits != self.num_qubits or body.num_clbits != self.num_clbits: raise CircuitError( "Attempted to assign a body parameter with a num_qubits or " "num_clbits different than that of the ForLoopOp. " f"ForLoopOp num_qubits/clbits: {self.num_qubits}/{self.num_clbits} " f"Supplied body num_qubits/clbits: {body.num_qubits}/{body.num_clbits}." ) if ( loop_parameter is not None and loop_parameter not in body.parameters and loop_parameter.name in (p.name for p in body.parameters) ): warnings.warn( "The Parameter provided as a loop_parameter was not found " "on the loop body and so no binding of the indexset to loop " "parameter will occur. A different Parameter of the same name " f"({loop_parameter.name}) was found. If you intended to loop " "over that Parameter, please use that Parameter instance as " "the loop_parameter.", stacklevel=2, ) # Consume indexset into a tuple unless it was provided as a range. # Preserve ranges so that they can be exported as OpenQASM 3 ranges. indexset = indexset if isinstance(indexset, range) else tuple(indexset) self._params = [indexset, loop_parameter, body] @property def blocks(self): return (self._params[2],)
[documentos] def replace_blocks(self, blocks): (body,) = blocks return ForLoopOp(self.params[0], self.params[1], body, label=self.label)
class ForLoopContext: """A context manager for building up ``for`` loops onto circuits in a natural order, without having to construct the loop body first. Within the block, a lot of the bookkeeping is done for you; you do not need to keep track of which qubits and clbits you are using, for example, and a loop parameter will be allocated for you, if you do not supply one yourself. All normal methods of accessing the qubits on the underlying :obj:`~QuantumCircuit` will work correctly, and resolve into correct accesses within the interior block. You generally should never need to instantiate this object directly. Instead, use :obj:`.QuantumCircuit.for_loop` in its context-manager form, i.e. by not supplying a ``body`` or sets of qubits and clbits. Example usage:: import math from qiskit import QuantumCircuit qc = QuantumCircuit(2, 1) with qc.for_loop(range(5)) as i: qc.rx(i * math.pi/4, 0) qc.cx(0, 1) qc.measure(0, 0) qc.break_loop().c_if(0, True) This context should almost invariably be created by a :meth:`.QuantumCircuit.for_loop` call, and the resulting instance is a "friend" of the calling circuit. The context will manipulate the circuit's defined scopes when it is entered (by pushing a new scope onto the stack) and exited (by popping its scope, building it, and appending the resulting :obj:`.ForLoopOp`). .. warning:: This is an internal interface and no part of it should be relied upon outside of Qiskit Terra. """ # Class-level variable keep track of the number of auto-generated loop variables, so we don't # get naming clashes. _generated_loop_parameters = 0 __slots__ = ( "_circuit", "_generate_loop_parameter", "_loop_parameter", "_indexset", "_label", "_used", ) def __init__( self, circuit: QuantumCircuit, indexset: Iterable[int], loop_parameter: Optional[Parameter] = None, *, label: Optional[str] = None, ): self._circuit = circuit self._generate_loop_parameter = loop_parameter is None self._loop_parameter = loop_parameter # We can pass through `range` instances because OpenQASM 3 has native support for this type # of iterator set. self._indexset = indexset if isinstance(indexset, range) else tuple(indexset) self._label = label self._used = False def __enter__(self): if self._used: raise CircuitError("A for-loop context manager cannot be re-entered.") self._used = True self._circuit._push_scope() if self._generate_loop_parameter: self._loop_parameter = Parameter(f"_loop_i_{self._generated_loop_parameters}") type(self)._generated_loop_parameters += 1 return self._loop_parameter def __exit__(self, exc_type, exc_val, exc_tb): if exc_type is not None: # If we're leaving the context manager because an exception was raised, there's nothing # to do except restore the circuit state. self._circuit._pop_scope() return False scope = self._circuit._pop_scope() # Loops do not need to pass any further resources in, because this scope itself defines the # extent of ``break`` and ``continue`` statements. body = scope.build(scope.qubits, scope.clbits) # We always bind the loop parameter if the user gave it to us, even if it isn't actually # used, because they requested we do that by giving us a parameter. However, if they asked # us to auto-generate a parameter, then we only add it if they actually used it, to avoid # using unnecessary resources. if self._generate_loop_parameter and self._loop_parameter not in body.parameters: loop_parameter = None else: loop_parameter = self._loop_parameter self._circuit.append( ForLoopOp(self._indexset, loop_parameter, body, label=self._label), tuple(body.qubits), tuple(body.clbits), ) return False