Talks

GitHub Actions

Harry Swift

Research Software Engineer

An introduction to GitHub Actions, covering the basics of setting up workflows, common use cases, and best practices for automating tasks in your repositories.

GitHub Actions is a CI/CD platform built into GitHub that lets you automate workflows such as testing, building, and deploying code. You define workflows using YAML files stored in your repository under .github/workflows/.

Prerequisites

Git installed
Python installed
GitHub CLI (gh) installed and logged in

Create a New Project Directory and Initialize Git

Terminal

mkdir python-ci-demo
cd python-ci-demo
git init

Create Python app and tests

Create the directory structure and files:

Terminal

mkdir -p app tests .github/workflows

Create app/main.py with a simple function:

app/main.py

def add(x, y):
    return x + y

Create tests/test_main.py with a test case:

tests/test_main.py

from app.main import add

def test_add():
    assert add(2, 3) == 5

Create requirements.txt listing dependencies:

requirements.txt

pytest
black

Add the Workflow YAML

Create .github/workflows/ci.yml with the following contents:

.github/workflows/ci.yml

name: Python CI
on: [push, pull_request]
jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: [3.11, 3.12, 3.13]
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4
      - name: Set up Python ${{ matrix.python-version }}
        uses: actions/setup-python@v5
        with:
          python-version: ${{ matrix.python-version }}
      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          pip install -r requirements.txt
      - name: Run tests
        run: |
          pytest
      - name: Check formatting with Black
        run: |
          black --check .

Adding Github Actions Workflow

Terminal

git add .
git commit -m "Initial commit with Python app and GitHub Actions CI"
gh repo create python-ci-demo --public --source=. --push

View your Workflow

Open your browser to your new repo, e.g.: https://github.com/YOUR_USERNAME/python-ci-demo

Click on thee "Actions" tab and observe the workflow running for each push or pull request.

Create CRON Jobs

Create .github/workflows/cron.yml with the following contents:

.github/workflows/cron.yml

name: Python CI

on:
  push:
  pull_request:
  schedule:
    - cron: '0 9 * * 1'  # Every Monday at 09:00 UTC

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: [3.11, 3.12, 3.13]
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4
      - name: Set up Python ${{ matrix.python-version }}
        uses: actions/setup-python@v5
        with:
          python-version: ${{ matrix.python-version }}
      - name: Install dependencies
        run: |
          python -m pip install --upgrade pip
          pip install -r requirements.txt
      - name: Run tests
        run: |
          pytest
      - name: Check formatting with Black
        run: |
          black --check .

What does 0 9 * * 1 mean?

Field	Value	Meaning
Minute	0	At the 0th minute
Hour	9	At 09:00 (9 AM UTC)
Day of Month	*	Every day
Month	*	Every month
Day of Week	1	Monday (0 = Sunday, 1 = Monday, ...)

This tells GitHub Actions to run the workflow every Monday at 9:00 AM UTC.

Spack

A live demo introduction to Spack, a package manager designed for high-performance computing (HPC) environments.

Inheritance is Evil

A talk discussing the problems with inheritance in object-oriented programming and advocating for composition over inheritance.