---
title: ForLoopOp (v0.46)
description: API reference for qiskit.circuit.ForLoopOp in qiskit v0.46
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit/0.46/qiskit.circuit.ForLoopOp
---

# ForLoopOp

*class* `qiskit.circuit.ForLoopOp(indexset, loop_parameter, body, label=None)`

[GitHub](https://github.com/qiskit/qiskit/tree/stable/0.46/qiskit/circuit/controlflow/for_loop.py)

Bases: [`ControlFlowOp`](/docs/api/qiskit/0.46/qiskit.circuit.ControlFlowOp "qiskit.circuit.controlflow.control_flow.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** ([*Iterable*](https://docs.python.org/3/library/typing.html#typing.Iterable)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*]*) – A collection of integers to loop over.
- **loop\_parameter** ([*Parameter*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.parameter.Parameter") *| None*) – The placeholder parameterizing `body` to which the values from `indexset` will be assigned.
- **body** ([*QuantumCircuit*](/docs/api/qiskit/0.46/qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")) – The loop body to be repeatedly executed.
- **label** ([*str*](https://docs.python.org/3/library/stdtypes.html#str) *| None*) – An optional label for identifying the instruction.

**Circuit symbol:**

```python
     ┌───────────┐
q_0: ┤0          ├
     │           │
q_1: ┤1          ├
     │  for_loop │
q_2: ┤2          ├
     │           │
c_0: ╡0          ╞
     └───────────┘
```

Create a new instruction.

**Parameters**

- **name** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – instruction name
- **num\_qubits** ([*int*](https://docs.python.org/3/library/functions.html#int)) – instruction’s qubit width
- **num\_clbits** ([*int*](https://docs.python.org/3/library/functions.html#int)) – instruction’s clbit width
- **params** ([*list*](https://docs.python.org/3/library/stdtypes.html#list)*\[*[*int*](https://docs.python.org/3/library/functions.html#int)*|*[*float*](https://docs.python.org/3/library/functions.html#float)*|*[*complex*](https://docs.python.org/3/library/functions.html#complex)*|*[*str*](https://docs.python.org/3/library/stdtypes.html#str)*|ndarray|*[*list*](https://docs.python.org/3/library/stdtypes.html#list)*|*[*ParameterExpression*](/docs/api/qiskit/0.46/qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression")*]*) – list of parameters
- **duration** ([*int*](https://docs.python.org/3/library/functions.html#int)  *or*[*float*](https://docs.python.org/3/library/functions.html#float)) – instruction’s duration. it must be integer if `unit` is ‘dt’
- **unit** ([*str*](https://docs.python.org/3/library/stdtypes.html#str)) – time unit of duration
- **label** ([*str*](https://docs.python.org/3/library/stdtypes.html#str) *or None*) – An optional label for identifying the instruction.

**Raises**

- [**CircuitError**](/docs/api/qiskit/0.46/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – when the register is not in the correct format.
- [**TypeError**](https://docs.python.org/3/library/exceptions.html#TypeError) – when the optional label is provided, but it is not a string.

## 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 behavioural perspective. In particular, you should *not* override [`base_class`](#qiskit.circuit.ForLoopOp.base_class "qiskit.circuit.ForLoopOp.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 parametrised gate with a particular set of parameters for the purposes of distinguishing it in a [`Target`](/docs/api/qiskit/0.46/qiskit.transpiler.Target "qiskit.transpiler.Target") from the full parametrised 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/0.46/qiskit.circuit.Instruction#name "qiskit.circuit.Instruction.name") should be a more suitable discriminator in most situations.

### blocks

### condition

The classical condition on the instruction.

### condition\_bits

Get Clbits in condition.

### decompositions

Get the decompositions of the instruction from the SessionEquivalenceLibrary.

### definition

Return definition in terms of other basic gates.

### duration

Get the duration.

### 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

### unit

Get the time unit of duration.

## Methods

### add\_decomposition

`add_decomposition(decomposition)`

Add a decomposition of the instruction to the SessionEquivalenceLibrary.

### assemble

`assemble()`

Assemble a QasmQobjInstruction

### broadcast\_arguments

`broadcast_arguments(qargs, cargs)`

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/0.46/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.

### c\_if

`c_if(classical, val)`

Set a classical equality condition on this instruction between the register or cbit `classical` and value `val`.

> **Note**
>
> This is a setter method, not an additive one. Calling this multiple times will silently override any previously set condition; it does not stack.

### copy

`copy(name=None)`

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/0.46/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

### inverse

`inverse()`

Invert this instruction.

If the instruction is composite (i.e. has a definition), then its definition will be recursively inverted.

Special instructions inheriting from Instruction can implement their own inverse (e.g. T and Tdg, Barrier, etc.)

**Returns**

a fresh instruction for the inverse

**Return type**

[qiskit.circuit.Instruction](/docs/api/qiskit/0.46/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

**Raises**

[**CircuitError**](/docs/api/qiskit/0.46/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()`

Return True .IFF. instruction is parameterized else False

### qasm

`qasm()`

Return a default OpenQASM string for the instruction.

Derived instructions may override this to print in a different format (e.g. `measure q[0] -> c[0];`).

> **Deprecated since version 0.25.0**
>
> The method `qiskit.circuit.instruction.Instruction.qasm()` is deprecated as of qiskit-terra 0.25.0. It will be removed in the Qiskit 1.0 release. Correct exporting to OpenQASM 2 is the responsibility of a larger exporter; it cannot safely be done on an object-by-object basis without context. No replacement will be provided, because the premise is wrong.

### repeat

`repeat(n)`

Creates an instruction with `self` repeated :math\`n\` times.

If this operation has a conditional, the output instruction will have the same conditional and the inner repeated operations will be unconditional; instructions within a compound definition cannot be conditioned on registers within Qiskit’s data model. This means that it is not valid to apply a repeated instruction to a clbit that it both writes to and reads from in its condition.

**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/0.46/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

**Raises**

[**CircuitError**](/docs/api/qiskit/0.46/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – If n \< 1.

### replace\_blocks

`replace_blocks(blocks)`

Replace blocks and return new instruction. :param blocks: Tuple of QuantumCircuits to replace in instruction.

**Returns**

New ControlFlowOp with replaced blocks.

### reverse\_ops

`reverse_ops()`

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/0.46/qiskit.circuit.Instruction "qiskit.circuit.Instruction")

### soft\_compare

`soft_compare(other)`

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()`

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)`

Instruction parameters has no validation or normalization.