---
title: ZeroPostSelect (latest version)
description: API reference for qiskit_noise_learning.analysis.ZeroPostSelect in the latest version of qiskit-noise-learning
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-noise-learning/generated/analysis-zero-post-select
---

# qiskit\_noise\_learning.analysis.ZeroPostSelect

*class* `qiskit_noise_learning.analysis.ZeroPostSelect(creg_identifier: Callable[[list[str]], Iterator[str]] | None = None, mode: Literal['node', 'edge'] = 'edge')`

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

Bases: [`AnalysisStage`](/docs/api/qiskit-noise-learning/generated/analysis-analysis-stage "qiskit_noise_learning.analysis.analysis_pipeline.AnalysisStage")

Apply a mask to raw data based on whether bit values are all False.

This post-selection stage identifies cregs and masks shots whose bit patterns indicate failure. It can be configured to operate in one of two modes:

- `"node"`: Shots are discarded if any bit in the identified creg is True.

- **`"edge"`: Shots are discarded if there exists a pair of neighbouring qubits in the**

  coupling map for which both bits are True.

**Parameters**

- **creg\_identifier** – A callable that, given a list of present creg names, returns an iterator over creg names to post-select on. Defaults to identifying cregs with naming pattern `"*_ps"`.
- **mode** – Post-selection mode; either `"node"` or `"edge"`.

### \_\_init\_\_

`__init__(creg_identifier: Callable[[list[str]], Iterator[str]] | None = None, mode: Literal['node', 'edge'] = 'edge')`

## Methods

|                                                                                                                                                           |                                                                                                                                                                       |
| --------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [`__init__`](#qiskit_noise_learning.analysis.ZeroPostSelect.__init__ "qiskit_noise_learning.analysis.ZeroPostSelect.__init__")(\[creg\_identifier, mode]) |                                                                                                                                                                       |
| `run`(fit)                                                                                                                                                | Run this stage, returning a new [`Fit`](/docs/api/qiskit-noise-learning/generated/analysis-fit "qiskit_noise_learning.analysis.Fit") with the output level populated. |

## Attributes

|                                                                                                                                            |                                   |
| ------------------------------------------------------------------------------------------------------------------------------------------ | --------------------------------- |
| `creg_identifier`                                                                                                                          |                                   |
| [`input_level`](#qiskit_noise_learning.analysis.ZeroPostSelect.input_level "qiskit_noise_learning.analysis.ZeroPostSelect.input_level")    | The data level this stage reads.  |
| `mode`                                                                                                                                     |                                   |
| [`output_level`](#qiskit_noise_learning.analysis.ZeroPostSelect.output_level "qiskit_noise_learning.analysis.ZeroPostSelect.output_level") | The data level this stage writes. |

### input\_level

The data level this stage reads.

### output\_level

The data level this stage writes.