werr 0.3.0

A python project task runner

werr

A simple, opinionated, python project task runner.

A task is a configured sequence of commands to run.

[project]
name = "appletree"
version = "0.1.0"
dependencies = [
    "pysunlight==24.1",
]

[tool.werr]
# 'check' is the default task if `werr` is run with no arguments.
task.check = [
    "black --check {project}",
    "isort --check {project}",
    "ruff check {project}",
    "mypy {project}",
    "pytest",
]
task.fix = [
    "black {project}",
    "isort {project}",
    "ruff fix {project}",
]

Running werr executes each check command in sequence, printing which failed and how. The tool returns a non-zero exit code if any command fails.

Running werr fix executes each fix command in sequence.

NOTE: All commands are run using uv (the only dependency of this project).

Command Variables

The following {...} variables are provided by werr to be used in task commands:

• {project} - the absolute path to the directory containing the pyproject.toml file

Structured Output

werr         # interactive human readable output (default)
werr --json  # emit lines of JSON representing the result of each command
werr --xml   # print Junit XML for CI

The --json output results in a line of JSON being emitted as soon as a command finishes:

> werr --json | jq
{
  "task": "black",
  "command": "black --check {project}/werrlib",
  "duration": 0.10738483420573175,
  "output": "All done! ✨ 🍰 ✨\n8 files would be left unchanged.\n",
  "success": true
}
{
  "task": "ruff",
  "command": "ruff check {project}/werrlib",
  "duration": 0.016670041950419545,
  "output": "All checks passed!\n",
  "success": true
}
{
  "task": "ty",
  "command": "ty check {project}/werrlib",
  "duration": 0.03577654203400016,
  "output": "All checks passed!\n",
  "success": true
}
{
  "task": "pytest",
  "command": "pytest --config-file {project}/pyproject.toml",
  "duration": 0.13576683308929205,
  "output": "============================= test session starts ==============================\nplatform darwin -- Python 3.14.0rc1, pytest-9.0.2, pluggy-1.6.0\nrootdir: /Users/joe/repos/werr\nconfigfile: pyproject.toml\ntestpaths: tests\ncollected 7 items\n\ntests/test_config.py .......                                             [100%]\n\n============================== 7 passed in 0.01s ===============================\n",
  "success": true
}

Custom Tasks

Define a custom task with task.<name> = [ ... ]

[tool.werr]
# ...
task.docs = [
    "sphinx-build -b html {project}",
]

Running werr docs will build the documentation.

New Project

A suggested workflow for creating a new project is:

1. uv init
2. uv add --dev black ruff ty pytest
3. add tasks to [tool.werr]
4. uvx werr or add to dev group and in venv just werr

Failing Example