---
title: suffix_creg_identifier (latest version)
description: API reference for qiskit_noise_learning.analysis.suffix_creg_identifier in the latest version of qiskit-noise-learning
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-noise-learning/generated/analysis-suffix-creg-identifier
---

# qiskit\_noise\_learning.analysis.suffix\_creg\_identifier

`qiskit_noise_learning.analysis.suffix_creg_identifier(suffix: str = '_ps') → Callable[[list[str]], Iterator[tuple[str, ...]]]`

[GitHub](https://github.com/Qiskit/qiskit-noise-learning/tree/stable/0.1/qiskit_noise_learning/analysis/flip_post_select.py)

Return a creg identifier that pairs each creg named `"*<suffix>"` with `"*"`.

The returned callable is suitable as the `creg_identifier` argument of [`FlipPostSelect`](/docs/api/qiskit-noise-learning/generated/analysis-flip-post-select "qiskit_noise_learning.analysis.FlipPostSelect"), and is the default that class uses. Given the names of the cregs present in a dataset, it yields one tuple for every name ending in `suffix`: the pair `(base, name)` when the corresponding `base` name is also present, and the singleton `(name,)` when it is not. Names that do not end in `suffix` are not post-selected on.

**Parameters**

**suffix** – The complete creg name suffix marking a post-selection register, including any separator. The default pairs `"meas_ps"` with `"meas"`.

**Returns**

A callable mapping a list of creg names to an iterator over groups of creg names.

**Raises**

[**ValueError**](https://docs.python.org/3/builtins/exceptions.html#ValueError) – If *suffix* is empty, which would pair every creg with itself.