---
title: BoxOp (latest version)
description: API reference for qiskit.circuit.BoxOp in the latest version of qiskit
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/qiskit.circuit.BoxOp
---

# BoxOp

*class* `qiskit.circuit.BoxOp(body, duration=None, unit=None, label=None, annotations=())`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/controlflow/box.py#L28-L133)

Bases: [`ControlFlowOp`](/docs/api/qiskit/qiskit.circuit.ControlFlowOp "qiskit.circuit.controlflow.control_flow.ControlFlowOp")

A scoped “box” of operations on a circuit that are treated atomically in the greater context.

A “box” is a control-flow construct that is entered unconditionally. The contents of the box behave somewhat as if the start and end of the box were barriers, except it is permissible to commute operations “all the way” through the box. The box is also an explicit scope for the purposes of variables, stretches and compiler passes.

A box may be “annotated” with arbitrary user-defined custom [`Annotation`](/docs/api/qiskit/qiskit.circuit.Annotation "qiskit.circuit.Annotation") objects. In cases where order is important, these should be interpreted by applying the first annotation in the list first, then the second, and so on. It is generally recommended that annotations should not be order-dependent, wherever possible.

Typically you create this by using the builder-interface form of [`QuantumCircuit.box()`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#box "qiskit.circuit.QuantumCircuit.box").

Default constructor of [`BoxOp`](#qiskit.circuit.BoxOp "qiskit.circuit.BoxOp").

**Parameters**

- **body** ([*QuantumCircuit*](/docs/api/qiskit/qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit")) – the circuit to use as the body of the box. This should explicitly close over any [`expr.Var`](/docs/api/qiskit/circuit_classical#qiskit.circuit.classical.expr.Var "qiskit.circuit.classical.expr.Var") variables that must be incident from the outer circuit. The required number of qubits and clbits for the resulting instruction are inferred from the number in the circuit, even if they are idle.
- **duration** (*None*) – an optional duration for the box as a whole.
- **unit** ([*Literal*](https://docs.python.org/3/library/typing.html#typing.Literal)*\['dt', 's', 'ms', 'us', 'ns', 'ps', 'expr'] | None*) – the unit of the `duration`.
- **label** ([*str*](https://docs.python.org/3/library/stdtypes.html#str) *| None*) – an optional string label for the instruction.
- **annotations** ([*Iterable*](https://docs.python.org/3/library/typing.html#typing.Iterable)*\[*[*Annotation*](/docs/api/qiskit/qiskit.circuit.Annotation "qiskit.circuit.Annotation")*]*) – any [`Annotation`](/docs/api/qiskit/qiskit.circuit.Annotation "qiskit.circuit.Annotation")s to apply to the box. In cases where order is important, annotations are to be interpreted in the same order they appear in the iterable.

## Attributes

### base\_class

Get the base class of this instruction. This is guaranteed to be in the inheritance tree of `self`.

The “base class” of an instruction is the lowest class in its inheritance tree that the object should be considered entirely compatible with for \_all\_ circuit applications. This typically means that the subclass is defined purely to offer some sort of programmer convenience over the base class, and the base class is the “true” class for a behavioral perspective. In particular, you should *not* override [`base_class`](#qiskit.circuit.BoxOp.base_class "qiskit.circuit.BoxOp.base_class") if you are defining a custom version of an instruction that will be implemented differently by hardware, such as an alternative measurement strategy, or a version of a parametrized gate with a particular set of parameters for the purposes of distinguishing it in a [`Target`](/docs/api/qiskit/qiskit.transpiler.Target "qiskit.transpiler.Target") from the full parametrized gate.

This is often exactly equivalent to `type(obj)`, except in the case of singleton instances of standard-library instructions. These singleton instances are special subclasses of their base class, and this property will return that base. For example:

```python
>>> isinstance(XGate(), XGate)
True
>>> type(XGate()) is XGate
False
>>> XGate().base_class is XGate
True
```

In general, you should not rely on the precise class of an instruction; within a given circuit, it is expected that [`Instruction.name`](/docs/api/qiskit/qiskit.circuit.Instruction#name "qiskit.circuit.Instruction.name") should be a more suitable discriminator in most situations.

### blocks

### body

The `body` [`QuantumCircuit`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit "qiskit.circuit.QuantumCircuit") of the operation.

This is the same object returned as the sole entry in [`params()`](#qiskit.circuit.BoxOp.params "qiskit.circuit.BoxOp.params") and [`blocks()`](#qiskit.circuit.BoxOp.blocks "qiskit.circuit.BoxOp.blocks").

### decompositions

Get the decompositions of the instruction from the SessionEquivalenceLibrary.

### definition

Return definition in terms of other basic gates.

### label

Return instruction label

### mutable

Is this instance is a mutable unique instance or not.

If this attribute is `False` the gate instance is a shared singleton and is not mutable.

### name

Return the name.

### num\_clbits

Return the number of clbits.

### num\_qubits

Return the number of qubits.

### params

## Methods

### add\_decomposition

`add_decomposition(decomposition)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L318-L323)

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

### broadcast\_arguments

`broadcast_arguments(qargs, cargs)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L452-L481)

Validation of the arguments.

**Parameters**

- **qargs** (*List*) – List of quantum bit arguments.
- **cargs** (*List*) – List of classical bit arguments.

**Yields**

*Tuple(List, List)* – A tuple with single arguments.

**Raises**

[**CircuitError**](/docs/api/qiskit/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – If the input is not valid. For example, the number of arguments does not match the gate expectation.

### copy

`copy(name=None)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L428-L443)

Copy of the instruction.

**Parameters**

**name** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – name to be given to the copied circuit, if `None` then the name stays the same.

**Returns**

a copy of the current instruction, with the name updated if it was provided

**Return type**

[qiskit.circuit.Instruction](/docs/api/qiskit/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

### inverse

`inverse(annotated=False)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L371-L426)

Invert this instruction.

If annotated is False, the inverse instruction is implemented as a fresh instruction with the recursively inverted definition.

If annotated is True, the inverse instruction is implemented as [`AnnotatedOperation`](/docs/api/qiskit/qiskit.circuit.AnnotatedOperation "qiskit.circuit.AnnotatedOperation"), and corresponds to the given instruction annotated with the “inverse modifier”.

Special instructions inheriting from Instruction can implement their own inverse (e.g. T and Tdg, Barrier, etc.) In particular, they can choose how to handle the argument `annotated` which may include ignoring it and always returning a concrete gate class if the inverse is defined as a standard gate.

**Parameters**

**annotated** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – if set to True the output inverse gate will be returned as [`AnnotatedOperation`](/docs/api/qiskit/qiskit.circuit.AnnotatedOperation "qiskit.circuit.AnnotatedOperation").

**Returns**

The inverse operation.

**Raises**

[**CircuitError**](/docs/api/qiskit/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – if the instruction is not composite and an inverse has not been implemented for it.

### is\_parameterized

`is_parameterized()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L283-L288)

Return whether the [`Instruction`](/docs/api/qiskit/qiskit.circuit.Instruction "qiskit.circuit.Instruction") contains [compile-time parameters](/docs/api/qiskit/circuit#circuit-compile-time-parameters).

### iter\_captured\_stretches

`iter_captured_stretches()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/controlflow/control_flow.py#L80-L88)

Get an iterator over the unique captured stretch variables in all blocks of this construct.

**Return type**

[*Iterable*](https://docs.python.org/3/library/typing.html#typing.Iterable)\[[expr.Stretch](/docs/api/qiskit/circuit_classical#qiskit.circuit.classical.expr.Stretch "qiskit.circuit.classical.expr.Stretch")]

### iter\_captured\_vars

`iter_captured_vars()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/controlflow/control_flow.py#L71-L78)

Get an iterator over the unique captured variables in all blocks of this construct.

**Return type**

[*Iterable*](https://docs.python.org/3/library/typing.html#typing.Iterable)\[[expr.Var](/docs/api/qiskit/circuit_classical#qiskit.circuit.classical.expr.Var "qiskit.circuit.classical.expr.Var")]

### repeat

`repeat(n)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L491-L521)

Creates an instruction with `self` repeated $n$ times.

**Parameters**

**n** ([*int*](https://docs.python.org/3/library/functions.html#int)) – Number of times to repeat the instruction

**Returns**

Containing the definition.

**Return type**

[qiskit.circuit.Instruction](/docs/api/qiskit/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

**Raises**

[**CircuitError**](/docs/api/qiskit/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – If n \< 1.

### replace\_blocks

`replace_blocks(blocks)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/controlflow/box.py#L116-L124)

Return a new version of this control-flow operations with the [`blocks`](#qiskit.circuit.BoxOp.blocks "qiskit.circuit.BoxOp.blocks") mapped to the given new ones.

Typically this is used in a workflow such as:

```python
existing_op = ...

def map_block(block: QuantumCircuit) -> QuantumCircuit:
    new_block = block.copy_empty_like()
    # ... do something to `new_block` ...
    return new_block

new_op = existing_op.replace_blocks(
    map_block(block) for block in existing_op.blocks
)
```

It is the caller’s responsibility to ensure that the mapped blocks are defined over a unified set of circuit resources, much like constructing a [`ControlFlowOp`](/docs/api/qiskit/qiskit.circuit.ControlFlowOp "qiskit.circuit.ControlFlowOp") using its default constructor.

**Parameters**

**blocks** – the new subcircuit blocks to use.

**Returns**

New [`ControlFlowOp`](/docs/api/qiskit/qiskit.circuit.ControlFlowOp "qiskit.circuit.ControlFlowOp") with replaced blocks.

### reverse\_ops

`reverse_ops()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L345-L369)

For a composite instruction, reverse the order of sub-instructions.

This is done by recursively reversing all sub-instructions. It does not invert any gate.

**Returns**

**a new instruction with**

sub-instructions reversed.

**Return type**

[qiskit.circuit.Instruction](/docs/api/qiskit/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

### soft\_compare

`soft_compare(other)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L214-L254)

Soft comparison between gates. Their names, number of qubits, and classical bit numbers must match. The number of parameters must match. Each parameter is compared. If one is a ParameterExpression then it is not taken into account.

**Parameters**

**other** (*instruction*) – other instruction.

**Returns**

are self and other equal up to parameter expressions.

**Return type**

[bool](https://docs.python.org/3/library/functions.html#bool)

### to\_mutable

`to_mutable()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L144-L152)

Return a mutable copy of this gate.

This method will return a new mutable copy of this gate instance. If a singleton instance is being used this will be a new unique instance that can be mutated. If the instance is already mutable it will be a deepcopy of that instance.

### validate\_parameter

`validate_parameter(parameter)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/circuit/instruction.py#L279-L281)

Instruction parameter has no validation or normalization.