scafpy 2026.4.3.1

Scaffolding tool & application framework for Python projects.

Scaf

Build more, sweat less.

Scaf is an opinionated filesystem-based project builder and domain-action runner for devs who just want to keep things simple. It solves the easy problems in application development, so you can focus on the hard ones.

Usage

Note: Currently only bash is supported (use WSL or git bash on Windows).

Install scaf (can be in your user/system env, but a venv is recommended):

pip install git+http://scaf.sycdan.com

Initialize scaf in your project root:

scaf init

Add this to your .venvrc or .bashrc file:

scaf discover . && source .scaf/aliases

Invoke an action (this will create it and add an alias, if it does not exist):

scaf call example/world/greet

Dev Server

Start the local dev server to run and test your domain actions from a browser UI:

scaf serve .

Then open http://localhost:54545.

Select an action, enter a JSON payload, choose which tests to run and whether you expect each to pass or fail, then hit Submit. The server saves the payload as a fixture in the action's fixtures/ folder and runs the selected tests in-process, returning live results. The server also hot-reloads any .py files under the deck as you edit them — no restart needed.

Additionally, you can launch the server with debugpy via VSCode's launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Debug dev server",
      "type": "debugpy",
      "request": "launch",
      "module": "scaf",
      "args": [
        "-vvv",
        "serve",
        "."
      ]
    }
  ]
}

Development

Keep dependencies to a minimum.

Use 2-space indentation in all Python files. Scaf's generated templates use 2-space indent, so consistency matters.

Environment Setup

source dev/env.sh [--nuke]

Note: If you change packages or hooks, nuke your env.

FAQ

How do I see verbose output from scaf calls?

Edit your .scaf/aliases file:

alias domain.action="scaf --vvv call $DECK/domain/action"
#                         ^ add this

Why am I getting Failed to load action package backend/domain/action: No module named 'domain'

Run scaf init in your app's PYTHONPATH directory (e.g. backend).

Why am I getting MyType | None is not callable?

You are probably on an old python version -- use Union[MyType, None] instead.

What is a venv?

A python virtual environment, allowing you to have project-specific dependencies. Create one thus:

python -m venv .venv

What is .venvrc?

A file intended to be sourced when your venv is activated. Typically placed in your project root.

Add this to the end of your venv activate script (e.g. .venv/Scripts/activate):

if [ -f "$VIRTUAL_ENV/"../.venvrc ]; then
  source "$VIRTUAL_ENV/"../.venvrc
fi