standalone-python-scripts

Standalone Python Scripts

Guidelines for writing single-file Python scripts that use PEP 723 inline metadata and uv for dependency management.

When to Use

• Creating a standalone Python script (single file, no pyproject.toml)
• Writing a CLI tool or utility script
• Building a quick automation or one-off script with external dependencies

NOT for: larger Python projects with multiple modules, packages, or a pyproject.toml/setup.py structure.

Procedure

1. Check Python version support — before setting requires-python, verify the target version is not end-of-life and has at least one year until EOL. Check https://devguide.python.org/versions/ for current status. Only target older versions if explicitly requested by the user.

2. Minimize dependencies — only add external packages that clearly save time or provide essential functionality. Prefer standard library when reasonable.

1. Add PEP 723 inline metadata — declare dependencies at the top of the script using the # /// script block format:

   # /// script
   # requires-python = ">=3.12"
   # dependencies = [
   #     "click>=8.1",
   #     "arrow>=1.3",
   # ]
   # ///
   

2. Use the uv shebang — when the script has non-stdlib dependencies, use:

   #!/usr/bin/env -S uv run --script
   

   This allows direct execution: ./script.py

3. Prefer Click for argument parsing — when the script needs CLI arguments, use Click over argparse or other libraries.

4. Prefer Arrow for date/time — when the script handles dates or times, use Arrow over datetime or other libraries.

5. Make executable — after creating the script, run chmod +x script.py to make it directly executable.

Example

#!/usr/bin/env -S uv run --script
# /// script
# requires-python = ">=3.12"
# dependencies = [
#     "click>=8.1",
#     "arrow>=1.3",
# ]
# ///

import click
import arrow

@click.command()
@click.option("--name", default="World", help="Name to greet")
@click.option("--date", is_flag=True, help="Show today's date")
def main(name, date):
    """Greet someone and optionally show the date."""
    click.echo(f"Hello, {name}!")
    if date:
        click.echo(f"Today is {arrow.now().format('YYYY-MM-DD')}")

if __name__ == "__main__":
    main()

Pitfalls

• Over-engineering: Don't add dependencies for trivial tasks. If datetime works, don't add Arrow. If argparse suffices, don't add Click.
• Missing shebang: Without #!/usr/bin/env -S uv run --script, the script won't run directly with ./script.py.
• Invalid metadata block: The # /// script block must be at the top and follow PEP 723 format exactly.
• Forgetting to chmod: The script needs execute permissions (chmod +x) to run directly.
• Version drift: Pin minimum versions in dependencies to avoid surprises when uv resolves packages.

Verification

After creating the script:

1. Check the metadata block is valid: uv run --script script.py --help
2. Run the script directly: ./script.py
3. Verify dependencies are installed and the script works as expected

Quick checklist:

Is the Python version still supported (not EOL, >1 year to EOL)?
Does the script have a shebang line?
Is the PEP 723 metadata block present and valid?
Are dependencies minimal and justified?
Is the script executable (chmod +x)?