Quellcode für qiskit.circuit.controlflow.while_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
# 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 ``while`` loop."

from typing import Optional, Tuple, Union

from qiskit.circuit import Clbit, ClassicalRegister, QuantumCircuit
from qiskit.circuit.exceptions import CircuitError
from .condition import validate_condition, condition_bits, condition_registers
from .control_flow import ControlFlowOp

[Doku]class WhileLoopOp(ControlFlowOp): """A circuit operation which repeatedly executes a subcircuit (``body``) until a condition (``condition``) evaluates as False. Parameters: condition: A condition to be checked prior to executing ``body``. Can be specified as either a tuple of a ``ClassicalRegister`` to be tested for equality with a given ``int``, or as a tuple of a ``Clbit`` to be compared to either a ``bool`` or an ``int``. body: The loop body to be repeatedly executed. label: An optional label for identifying the instruction. The classical bits used in ``condition`` must be a subset of those attached to ``body``. **Circuit symbol:** .. parsed-literal:: ┌─────────────┐ q_0: ┤0 ├ │ │ q_1: ┤1 ├ │ while_loop │ q_2: ┤2 ├ │ │ c_0: ╡0 ╞ └─────────────┘ """ def __init__( self, condition: Union[ Tuple[ClassicalRegister, int], Tuple[Clbit, int], Tuple[Clbit, bool], ], body: QuantumCircuit, label: Optional[str] = None, ): num_qubits = body.num_qubits num_clbits = body.num_clbits super().__init__("while_loop", num_qubits, num_clbits, [body], label=label) self.condition = validate_condition(condition) @property def params(self): return self._params @params.setter def params(self, parameters): (body,) = parameters if not isinstance(body, QuantumCircuit): raise CircuitError( "WhileLoopOp expects a body parameter 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 WhileLoopOp. " f"WhileLoopOp num_qubits/clbits: {self.num_qubits}/{self.num_clbits} " f"Supplied body num_qubits/clbits: {body.num_qubits}/{body.num_clbits}." ) self._params = [body] @property def blocks(self): return (self._params[0],)
[Doku] def replace_blocks(self, blocks): (body,) = blocks return WhileLoopOp(self.condition, body, label=self.label)
[Doku] def c_if(self, classical, val): raise NotImplementedError( "WhileLoopOp cannot be classically controlled through Instruction.c_if. " "Please use an IfElseOp instead." )
class WhileLoopContext: """A context manager for building up while 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. 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.while_loop` in its context-manager form, i.e. by not supplying a ``body`` or sets of qubits and clbits. Example usage:: from qiskit.circuit import QuantumCircuit, Clbit, Qubit bits = [Qubit(), Qubit(), Clbit()] qc = QuantumCircuit(bits) with qc.while_loop((bits[2], 0)): qc.h(0), 1) qc.measure(0, 0) .. warning:: This is an internal interface and no part of it should be relied upon outside of Qiskit Terra. """ __slots__ = ("_circuit", "_condition", "_label") def __init__( self, circuit: QuantumCircuit, condition: Union[ Tuple[ClassicalRegister, int], Tuple[Clbit, int], Tuple[Clbit, bool], ], *, label: Optional[str] = None, ): self._circuit = circuit self._condition = validate_condition(condition) self._label = label def __enter__(self): self._circuit._push_scope( clbits=condition_bits(self._condition), registers=condition_registers(self._condition) ) 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.clbits) self._circuit.append( WhileLoopOp(self._condition, body, label=self._label), body.qubits, body.clbits, ) return False