241 lines
7.5 KiB
Plaintext
241 lines
7.5 KiB
Plaintext
---
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title: Barrier
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description: API reference for qiskit.circuit.library.Barrier
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in_page_toc_min_heading_level: 1
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python_api_type: class
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python_api_name: qiskit.circuit.library.Barrier
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---
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# Barrier
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<Class id="qiskit.circuit.library.Barrier" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/circuit/barrier.py" signature="qiskit.circuit.library.Barrier(num_qubits, label=None)" modifiers="class">
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Bases: [`Instruction`](qiskit.circuit.Instruction "qiskit.circuit.instruction.Instruction")
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Barrier instruction.
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A barrier is a visual indicator of the grouping of a circuit section. It also acts as a directive for circuit compilation to separate pieces of a circuit so that any optimizations or re-writes are constrained to only act between barriers.
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Create new barrier instruction.
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**Parameters**
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* **num\_qubits** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – the number of qubits for the barrier type \[Default: 0].
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* **label** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – the barrier label
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**Raises**
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[**TypeError**](https://docs.python.org/3/library/exceptions.html#TypeError "(in Python v3.12)") – if barrier label is invalid.
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## Attributes
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### condition\_bits
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<Attribute id="qiskit.circuit.library.Barrier.condition_bits">
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Get Clbits in condition.
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</Attribute>
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### decompositions
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<Attribute id="qiskit.circuit.library.Barrier.decompositions">
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Get the decompositions of the instruction from the SessionEquivalenceLibrary.
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</Attribute>
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### definition
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<Attribute id="qiskit.circuit.library.Barrier.definition">
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Return definition in terms of other basic gates.
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</Attribute>
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### duration
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<Attribute id="qiskit.circuit.library.Barrier.duration">
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Get the duration.
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</Attribute>
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### label
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<Attribute id="qiskit.circuit.library.Barrier.label">
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Return instruction label
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</Attribute>
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### name
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<Attribute id="qiskit.circuit.library.Barrier.name">
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Return the name.
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</Attribute>
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### num\_clbits
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<Attribute id="qiskit.circuit.library.Barrier.num_clbits">
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Return the number of clbits.
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</Attribute>
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### num\_qubits
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<Attribute id="qiskit.circuit.library.Barrier.num_qubits">
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Return the number of qubits.
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</Attribute>
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### params
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<Attribute id="qiskit.circuit.library.Barrier.params">
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return instruction params.
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</Attribute>
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### unit
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<Attribute id="qiskit.circuit.library.Barrier.unit">
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Get the time unit of duration.
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</Attribute>
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## Methods
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### add\_decomposition
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<Function id="qiskit.circuit.library.Barrier.add_decomposition" signature="add_decomposition(decomposition)">
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Add a decomposition of the instruction to the SessionEquivalenceLibrary.
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</Function>
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### assemble
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<Function id="qiskit.circuit.library.Barrier.assemble" signature="assemble()">
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Assemble a QasmQobjInstruction
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</Function>
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### broadcast\_arguments
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<Function id="qiskit.circuit.library.Barrier.broadcast_arguments" signature="broadcast_arguments(qargs, cargs)">
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Validation of the arguments.
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**Parameters**
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* **qargs** (*List*) – List of quantum bit arguments.
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* **cargs** (*List*) – List of classical bit arguments.
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**Yields**
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*Tuple(List, List)* – A tuple with single arguments.
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**Raises**
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[**CircuitError**](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.
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</Function>
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### c\_if
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<Function id="qiskit.circuit.library.Barrier.c_if" signature="c_if(classical, val)">
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Set a classical equality condition on this instruction between the register or cbit `classical` and value `val`.
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<Admonition title="Note" type="note">
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This is a setter method, not an additive one. Calling this multiple times will silently override any previously set condition; it does not stack.
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</Admonition>
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</Function>
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### copy
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<Function id="qiskit.circuit.library.Barrier.copy" signature="copy(name=None)">
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Copy of the instruction.
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**Parameters**
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**name** ([*str*](https://docs.python.org/3/library/stdtypes.html#str "(in Python v3.12)")) – name to be given to the copied circuit, if `None` then the name stays the same.
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**Returns**
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a copy of the current instruction, with the name updated if it was provided
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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</Function>
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### inverse
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<Function id="qiskit.circuit.library.Barrier.inverse" signature="inverse()">
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Special case. Return self.
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</Function>
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### is\_parameterized
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<Function id="qiskit.circuit.library.Barrier.is_parameterized" signature="is_parameterized()">
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Return True .IFF. instruction is parameterized else False
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</Function>
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### qasm
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<Function id="qiskit.circuit.library.Barrier.qasm" signature="qasm()">
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Return a default OpenQASM string for the instruction.
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Derived instructions may override this to print in a different format (e.g. `measure q[0] -> c[0];`).
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<Admonition title="Deprecated since version 0.25.0" type="danger">
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The method `qiskit.circuit.instruction.Instruction.qasm()` is deprecated as of qiskit-terra 0.25.0. It will be removed no earlier than 3 months after the release date. 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.
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</Admonition>
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</Function>
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### repeat
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<Function id="qiskit.circuit.library.Barrier.repeat" signature="repeat(n)">
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Creates an instruction with gate repeated n amount of times.
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**Parameters**
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**n** ([*int*](https://docs.python.org/3/library/functions.html#int "(in Python v3.12)")) – Number of times to repeat the instruction
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**Returns**
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Containing the definition.
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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**Raises**
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[**CircuitError**](circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – If n \< 1.
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</Function>
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### reverse\_ops
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<Function id="qiskit.circuit.library.Barrier.reverse_ops" signature="reverse_ops()">
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For a composite instruction, reverse the order of sub-instructions.
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This is done by recursively reversing all sub-instructions. It does not invert any gate.
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**Returns**
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**a new instruction with**
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sub-instructions reversed.
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**Return type**
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[qiskit.circuit.Instruction](qiskit.circuit.Instruction "qiskit.circuit.Instruction")
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</Function>
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### soft\_compare
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<Function id="qiskit.circuit.library.Barrier.soft_compare" signature="soft_compare(other)">
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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.
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**Parameters**
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**other** (*instruction*) – other instruction.
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**Returns**
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are self and other equal up to parameter expressions.
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**Return type**
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[bool](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")
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</Function>
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### validate\_parameter
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<Function id="qiskit.circuit.library.Barrier.validate_parameter" signature="validate_parameter(parameter)">
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Instruction parameters has no validation or normalization.
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</Function>
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</Class>
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