Generate YAML with valohai-utils

If you prefer defining ML workflows in Python instead of writing YAML by hand, the Python helper tool valohai-utils lets you generate valohai.yaml from your code.

This is optional. Many users write YAML directly to keep their code free of Valohai dependencies.

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Why Generate YAML from Python?

Familiar syntax: If you're more comfortable with Python than YAML, this approach feels more natural.

Type safety: Python editors provide autocomplete and type checking, catching errors before execution.

Programmatic generation: Build YAML dynamically based on conditions, loops, or external configs.

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How It Works

Install valohai-utils:

pip install valohai-utils

Define a step in your Python script:

# train.py
import valohai

# Define parameters
params = {
    "epochs": 10,
    "learning_rate": 0.001,
}

# Define inputs
inputs = {
    "dataset": "s3://my-bucket/train.csv",
}

valohai.prepare(step="train", image="python:3.12", default_parameters=params, default_inputs=inputs)

# Your training code
print(f"Training with lr={lr} for {epochs} epochs")
print(f"Dataset: {dataset}")

Generate the YAML:

vh yaml step train.py

This creates the following valohai.yaml file:

- step:
    name: train
    image: python:3.12
    command: python train.py {parameters}
    parameters:
      - name: learning_rate
        default: 0.001
        type: float
      - name: epochs
        default: 10
        type: integer
    inputs:
      - name: dataset
        default: s3://my-bucket/train.csv

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When to Use This Approach

You're Python-first: Your team is more comfortable with Python than YAML syntax.

Dynamic workflows: You need to generate steps programmatically based on runtime conditions.

Rapid prototyping: You want to define and test steps quickly without switching between files.

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When NOT to Use This Approach

Keep code clean: If you want your ML code to remain framework-agnostic, write YAML by hand.

Team collaboration: Non-Python users may find YAML easier to read and edit.

Complex pipelines: Large multi-step pipelines are often clearer in YAML than generated from Python.

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What's Next?

• Validate your YAML with the linter

• Multiple YAML files for monorepo projects

• Manage large YAML files with anchors