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Fix documentation of SwitchCaseOp #10484

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Jul 24, 2023
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Fix documentation of SwitchCaseOp #10484

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38 changes: 35 additions & 3 deletions qiskit/circuit/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -296,9 +296,41 @@

The :class:`.SwitchCaseOp` also understands a special value:

.. py:data: CASE_DEFAULT
Used as a possible "label" in a :class:`.SwitchCaseOp` to represent the default case. This will
always match, if it is tried.
.. py:data:: CASE_DEFAULT

A special object that represents the "default" case of a switch statement. If you use this as a
case target, it must be the last case, and will match anything that wasn't already matched. For
example::

from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
from qiskit.circuit import SwitchCaseOp, CASE_DEFAULT

body0 = QuantumCircuit(2, 2)
body0.x(0)
body1 = QuantumCircuit(2, 2)
body1.z(0)
body2 = QuantumCircuit(2, 2)
body2.cx(0, 1)

qr, cr = QuantumRegister(2), ClassicalRegister(2)
qc = QuantumCircuit(qr, cr)
qc.switch(cr, [(0, body0), (1, body1), (CASE_DEFAULT, body2)], qr, cr)

When using the builder interface of :meth:`.QuantumCircuit.switch`, this can also be accessed as
the ``DEFAULT`` attribute of the bound case-builder object, such as::

from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister

qr, cr = QuantumRegister(2), ClassicalRegister(2)
qc = QuantumCircuit(qr, cr)
with qc.switch(cr) as case:
with case(0):
qc.x(0)
with case(1):
qc.z(0)
with case(case.DEFAULT):
qc.cx(0, 1)


Parametric Quantum Circuits
---------------------------
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7 changes: 3 additions & 4 deletions qiskit/circuit/controlflow/switch_case.py
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Expand Up @@ -41,8 +41,7 @@ def __repr__(self):
"""A special object that represents the "default" case of a switch statement. If you use this
as a case target, it must be the last case, and will match anything that wasn't already matched.
When using the builder interface of :meth:`.QuantumCircuit.switch`, this can also be accessed as the
``DEFAULT`` attribute of the bound case-builder object.
"""
``DEFAULT`` attribute of the bound case-builder object."""


class SwitchCaseOp(ControlFlowOp):
Expand All @@ -51,12 +50,12 @@ class SwitchCaseOp(ControlFlowOp):
be used to represent a default condition.

This is the low-level interface for creating a switch-case statement; in general, the circuit
method :meth:`.QuantumCircuit.switch_case` should be used as a context manager to access the
method :meth:`.QuantumCircuit.switch` should be used as a context manager to access the
builder interface. At the low level, you must ensure that all the circuit blocks contain equal
numbers of qubits and clbits, and that the order the virtual bits of the containing circuit
should be bound is the same for all blocks. This will likely mean that each circuit block is
wider than its natural width, as each block must span the union of all the spaces covered by
_any_ of the blocks.
*any* of the blocks.

Args:
target: the runtime value to switch on.
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