YAML Workflows

Modern CI uses YAML for declarative pipelines. Example (.github/workflows/ci.yml):

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: '3.12'
      - run: pip install -r requirements.txt
      - run: pytest

Key concepts:

• Workflow: top-level file. Triggers on events.
• Jobs: parallel units. Each runs on a fresh runner (VM or container).
• Steps: sequential within a job. Either run: <shell> or uses: <action>.
• Actions: reusable units (checkout, setup-X, deploy-Y) — community packages.

Triggers (on:):

• push, pull_request, release
• schedule: [{cron: "0 0 * * *"}]
• workflow_dispatch (manual)
• repository_dispatch (API-triggered)

Conditional execution:

- run: deploy.sh
  if: github.ref == 'refs/heads/main'

Matrix builds:

strategy:
  matrix:
    python-version: ['3.10', '3.11', '3.12']
    os: [ubuntu-latest, macos-latest, windows-latest]

That spawns 9 parallel jobs (3×3). Useful for cross-platform / cross-version testing.