Just (Python Wrapper)

1.49.0 · active · verified Sun Apr 12

rust-just is a Python wrapper for the `just` command runner, a powerful and simpler alternative to Make for project-specific task automation. It allows Python applications to programmatically invoke `just` recipes defined in a `Justfile`. The current version, 1.49.0, aligns with the version of the underlying `just` command-line tool, which maintains an active development cycle with frequent updates.

Warnings

gotcha The `rust-just` Python package acts as a wrapper for the `just` command-line executable. Installing `rust-just` via pip DOES NOT install the `just` binary itself. You must install the `just` command-line tool separately on your system for the wrapper to function.
Fix: Ensure the `just` executable is installed and available in your system's PATH. Refer to https://just.systems/#installation for detailed installation instructions for your operating system.
gotcha The version of the `rust-just` Python package typically mirrors the version of the underlying `just` command-line tool it is designed to wrap. While the Python wrapper's API is generally stable, functionality changes, new features, or breaking changes in the `just` tool's CLI (e.g., recipe syntax, new flags) will only be reflected if a compatible `just` binary is installed and the wrapper is updated.
Fix: Always check the `just` command-line tool's changelog (https://github.com/casey/just/releases) when upgrading or encountering unexpected behavior. Ensure your installed `just` binary matches the version expected by the Python wrapper for optimal compatibility.
gotcha If the `just` executable is not found in the system's PATH when `just_runner.run()` is called, it will raise a `subprocess.CalledProcessError` or `FileNotFoundError` (depending on the Python version and specific error scenario).
Fix: Verify that `just` is correctly installed and its directory is included in the system's PATH. You can test this by running `just --version` in your terminal.

Install

pip install rust-just Install Python wrapper
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash Install Just CLI (Linux/macOS)
choco install just Install Just CLI (Windows via Chocolatey)

Imports

Just
```
from just import Just
```
The PyPI package `rust-just` exposes the `Just` class directly under the `just` module name.

Quickstart

This quickstart demonstrates how to use the `rust-just` wrapper to execute recipes defined in a `Justfile`. It shows how to run a simple recipe, a recipe with arguments, and handles expected errors when recipes fail or don't exist. It also sets up a temporary `Justfile` for a runnable example.

import os
import subprocess

# Create a dummy Justfile for demonstration
justfile_content = """
hello:
  echo 'Hello from Just!'

greet NAME=\"World\":
  echo "Hello, {{NAME}}!"

fail:
  exit 1
"""

with open('Justfile', 'w') as f:
    f.write(justfile_content)

try:
    from just import Just
    just_runner = Just()

    print("Running 'hello' recipe:")
    result_hello = just_runner.run(recipe='hello')
    print(f"Output: {result_hello.stdout.strip()}\n")

    print("Running 'greet' recipe with argument:")
    result_greet = just_runner.run(recipe='greet', args=['NAME=Pythonista'])
    print(f"Output: {result_greet.stdout.strip()}\n")

    print("Attempting to run a non-existent recipe (expected error):")
    try:
        just_runner.run(recipe='non_existent')
    except subprocess.CalledProcessError as e:
        print(f"Caught expected error: {e.stderr.strip().splitlines()[0]} [...]")

    print("Attempting to run 'fail' recipe (expected error):")
    try:
        just_runner.run(recipe='fail')
    except subprocess.CalledProcessError as e:
        print(f"Caught expected error with return code {e.returncode}\n")

finally:
    # Clean up the dummy Justfile
    if os.path.exists('Justfile'):
        os.remove('Justfile')

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