---
title: ExperimentBuilderStage (latest version)
description: API reference for qiskit_noise_learning.experiment_builder.ExperimentBuilderStage in the latest version of qiskit-noise-learning
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-noise-learning/generated/experiment-builder-experiment-builder-stage
---

# qiskit\_noise\_learning.experiment\_builder.ExperimentBuilderStage

*class* `qiskit_noise_learning.experiment_builder.ExperimentBuilderStage`

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

Bases: [`ABC`](https://docs.python.org/3/library/abc.html#abc.ABC)

Abstract base for a stage in the experiment-building pipeline.

Each stage takes an [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") and returns a new [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") with additional fields populated or existing fields transformed.

Subclasses declare which [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") fields they require via the `required_fields` class attribute, and which fields they populate (can take form `None` to a non-`None` value) via `populates_fields`. The public [`run()`](#qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.run "qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.run") method validates that the required fields are not `None` before dispatching to `_run()`.

[`ExperimentBuilder`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment-builder "qiskit_noise_learning.experiment_builder.ExperimentBuilder") uses `populates_fields` to compute its aggregate `required_fields`: a stage’s requirement is satisfied if a preceding stage populates that field.

**Parameters**

- **required\_fields** – Tuple of [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") property names that must be non-`None` before this stage can execute.
- **populates\_fields** – Tuple of [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") property names that this stage populates on the returned [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment").

### \_\_init\_\_

`__init__()`

## Methods

|                                                                                                                                                                      |                                                  |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------ |
| [`__init__`](#qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.__init__ "qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.__init__")() |                                                  |
| [`run`](#qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.run "qiskit_noise_learning.experiment_builder.ExperimentBuilderStage.run")(experiment)      | Validate required fields, then apply this stage. |

## Attributes

|                    |   |
| ------------------ | - |
| `populates_fields` |   |
| `required_fields`  |   |

### run

`run(experiment: Experiment) → Experiment`

Validate required fields, then apply this stage.

**Parameters**

**experiment** – The input experiment.

**Returns**

A new [`Experiment`](/docs/api/qiskit-noise-learning/generated/experiment-builder-experiment "qiskit_noise_learning.experiment_builder.Experiment") with this stage’s transformations applied.

**Raises**

[**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError) – If any field listed in `required_fields` is `None`.