RubyPyMill

Running Notebooks the Ruby Way — RubyPyMill and the Art of PoC Automation

Background and Purpose

RubyPyMill is a lightweight runner and automation starter that allows Ruby to control Papermill (a Python Notebook runner).

Its purpose is to bridge insights born from Proof of Concept (PoC) work into real-world systems.

PoC is not the end — it is the beginning of organizational knowledge circulation.

By connecting Ruby’s expressive power with Python’s execution ecosystem, RubyPyMill enables a development cycle where teams collaborate with data in a Ruby-native way.

Design Philosophy — Inspired by Ruby 4.0 @30

RubyPyMill follows Ruby 4.0’s philosophy of “multi-language collaboration”.

Ruby is responsible for DSLs, orchestration, and control.
Python is responsible for execution, computation, and visualization via notebooks.

By clearly separating these roles and bridging them automatically, RubyPyMill enables reproducible notebook execution from the Ruby ecosystem.

“Ruby aims to connect people with people, and tools with tools.”
— Yukihiro “Matz” Matsumoto

Project Structure

Directory	Description
.vscode/	VS Code settings (extensions, lint/format, tasks, debug)
.github/workflows/	CI for Ruby and Python
bin/	CLI entry point (`ruby_pymill`)
lib/	RubyPyMill core library
py/	Python-side environment (Papermill execution)
examples/	Example notebooks, parameters, and outputs

Setup

Ruby

bundle install

Python

python -m venv .venv

# macOS / Linux
source .venv/bin/activate

# Windows (PowerShell)
.\.venv\Scripts\activate

pip install -r py/requirements.txt
python -m ipykernel install --user --name rpymill

Basic Usage (CLI)

bundle exec ruby bin/ruby_pymill exec <input.ipynb> \
  --output <output.ipynb> \
  [--kernel rpymill] \
  [--params params.json] \
  [--cell_tags "parameters,setup,analysis"] \
  [--dry-run]

Processing Overview

Load the notebook as JSON.
Filter cells by specified tags (the parameters cell is always preserved).
Generate a temporary filtered notebook.
Execute the filtered notebook once using Papermill.
Save the executed result as an output notebook.

RubyPyMill acts as a higher-level orchestration layer on top of Papermill, ensuring logical structure, reproducibility, and Ruby-friendly control.

Example: Ruby vs Python Radar Chart

The examples/ directory includes a notebook that compares Ruby and Python strengths using a radar chart.

This example demonstrates:

Parameter injection via JSON
Tag-based execution control
Separation of preview and output generation
Reproducible notebook execution via RubyPyMill

For a detailed explanation in Japanese, see README.jp.md.

Programmatic Usage (Experimental)

RubyPyMill is primarily designed as a CLI tool.

Internally, it exposes a Ruby execution API (RubyPyMill::API), which allows direct invocation from Ruby code.

This enables integration with batch jobs, schedulers, or future web APIs.

The CLI is considered the stable interface. The Ruby API is experimental and may change.