cliss 0.1.4

cliss — A lightweight framework for building CLI applications on top of argparse

cliss — A lightweight framework for building CLI applications on top of argparse

Write type-annotated Python functions, get a full CLI — automatic --help, validation, and async support with zero dependencies.

✨ Features

• 🪶 Zero Dependencies — Pure stdlib: argparse, asyncio, inspect
• 🏷️ Type-Driven — Automatic arguments from function signatures and type hints
• 🧩 Flexible — Declarative Argument objects, type inference, or both
• ⚡ Async-Native — async def handlers with automatic event loop management
• 🌍 Global Args — Define flags shared across all commands
• 🎨 Coloured Help — Automatic coloured output on Python 3.14+, ANSI fallback for older versions
• 🔧 argparse Access — Full access to underlying parsers for advanced use

🚀 Quick Start

Prerequisites

• Python 3.9+

Installation

Via pip (recommended)

pip install cliss

Via uv

uv pip install cliss

Via pipx (isolated environment)

pipx install cliss

From source (development)

git clone https://github.com/Fkernel653/cliss.git && cd cliss

pip

pip install .

uv

uv pip install .

pipx

pipx install .

Usage

from cliss import CLI

cli = CLI(
    name="todo",
    description="A simple task manager",
    version="1.0.0"
)

@cli.command()
def add(task: str, priority: int = 1, done: bool = False):
    """Add a new task to the list."""
    status = "✓" if done else "○"
    return f"[{status}] {task} (priority: {priority})"

@cli.command()
def list(filter: str = "all"):
    """List tasks. Use --filter to show pending/completed."""
    return f"Showing {filter} tasks"

if __name__ == "__main__":
    cli.run()

$ python todo.py add "Buy milk" --priority 2
[○] Buy milk (priority: 2)

$ python todo.py add "Call mom" --done --priority 3
[✓] Call mom (priority: 3)

$ python todo.py list --filter pending
Showing pending tasks

$ python todo.py --help
usage: todo [-h] [--version] {add,list} ...

A simple task manager

positional arguments:
  {add,list}   Commands
    add        Add a new task to the list.
    list       List tasks. Use --filter to show pending/completed.

options:
  -h, --help   show this help message and exit
  --version    show program's version number and exit

📋 Commands

CLI class

CLI(
    name="myapp",
    description="My CLI application",
    version="1.0.0",
    auto_help=True,
    colour=True
)

Parameter	Type	Default	Description
name	Optional[str]	None	Program name in help output
description	Optional[str]	None	Description in help output
version	Optional[str]	None	Adds --version flag
auto_help	bool	True	Adds --help flag
colour	bool	True	Enables coloured help output (Python 3.12+ native, else ANSI)

Argument class

from cliss import Argument

Argument(
    "--output", "-o",
    type=str,
    default=None,
    help="Output file path",
    required=False,
    choices=["json", "csv"],
    action="store_true"
)

Parameter	Type	Default	Description
*flags	str	—	Argument flags (e.g., --output, -o)
type	type	str	Value type for coercion
default	Any	None	Default value
help	str	""	Help text
required	bool	False	Make argument required
choices	Optional[List[Any]]	None	Restrict allowed values
action	Optional[str]	None	argparse action (store_true, store_false, etc.)

Type → CLI Mapping

Function Signature	CLI Argument	Behaviour
name: str	Positional name	Required positional argument
count: int = 1	--count	Optional with type int, default 1
verbose: bool = False	--verbose	Flag, store_true
quiet: bool = True	--quiet	Flag, store_false
items: list[str]	Positional items	Positional with type str
mode: Optional[str] = None	--mode	Optional with default None

📖 Examples

CRUD Application

from cliss import CLI

cli = CLI(name="db", description="Simple key-value store")
db = {}

@cli.command()
def set(key: str, value: str):
    """Store a value."""
    db[key] = value
    return f"OK: {key} = {value}"

@cli.command()
def get(key: str):
    """Retrieve a value."""
    return db.get(key, "Not found")

@cli.command()
def delete(key: str, force: bool = False):
    """Delete a key."""
    if force or key in db:
        db.pop(key, None)
        return f"Deleted: {key}"
    return f"Not found: {key} (use --force)"

if __name__ == "__main__":
    cli.run()

$ python db.py set name Alice
OK: name = Alice

$ python db.py get name
Alice

$ python db.py delete name
Deleted: name

$ python db.py delete missing --force
Deleted: missing

Explicit Arguments with Choices

from cliss import CLI, Argument

cli = CLI(name="convert", description="File format converter")

@cli.command(arguments=[
    Argument("input", help="Input file path"),
    Argument("--output", "-o", default="out.txt", help="Output file"),
    Argument("--format", "-f", choices=["json", "csv", "yaml"], default="json")
])
def convert(input: str, output: str = "out.txt", format: str = "json"):
    """Convert between file formats."""
    return f"Converting {input} -> {output} as {format}"

if __name__ == "__main__":
    cli.run()

$ python convert.py data.csv -o data.json -f json
Converting data.csv -> data.json as json

$ python convert.py data.csv -f xml
error: argument --format/-f: invalid choice: 'xml' (choose from 'json', 'csv', 'yaml')

Async Command Handlers

import asyncio
from cliss import CLI

cli = CLI(name="fetcher", description="Async data fetcher")

@cli.command()
async def fetch(url: str, retries: int = 3, timeout: float = 10.0):
    """Fetch data from URL asynchronously."""
    for attempt in range(retries):
        try:
            # Simulate async network request
            await asyncio.sleep(0.5)
            return f"Success: {url} (attempt {attempt + 1})"
        except Exception:
            if attempt == retries - 1:
                return f"Failed after {retries} attempts"
    return "Unknown error"

@cli.command()
async def parallel(urls: str, max_concurrent: int = 3):
    """Process multiple URLs in parallel."""
    url_list = urls.split(",")
    # Simulate parallel processing
    await asyncio.sleep(1)
    return f"Processed {len(url_list)} URLs with {max_concurrent} workers"

if __name__ == "__main__":
    cli.run()

Global Arguments

from cliss import CLI

cli = CLI(name="myapp", description="App with global flags")
cli.add_global_argument("--verbose", "-v", action="store_true", help="Verbose output")
cli.add_global_argument("--config", "-c", default="config.json", help="Config file")

@cli.command()
def status(verbose: bool = False):
    """Show application status."""
    return "Detailed status..." if verbose else "OK"

@cli.command()
def process(file: str, config: str = "config.json"):
    """Process a file with given config."""
    return f"Processing {file} with {config}"

if __name__ == "__main__":
    cli.run()

$ myapp status
OK

$ myapp --verbose status
Detailed status...

$ myapp --config prod.json process data.csv
Processing data.csv with prod.json

Mixing Explicit and Inferred Arguments

from cliss import CLI, Argument

cli = CLI(name="backup", description="Backup utility")

@cli.command(arguments=[
    Argument("--compress", "-z", action="store_true", help="Enable compression")
])
def backup(source: str, destination: str = "/backups", compress: bool = False):
    """Backup source directory to destination."""
    mode = "compressed" if compress else "uncompressed"
    return f"Backing up {source} -> {destination} ({mode})"

if __name__ == "__main__":
    cli.run()

$ python backup.py /home/user --compress
Backing up /home/user -> /backups (compressed)

$ python backup.py /var/www --destination /mnt/nas
Backing up /var/www -> /mnt/nas (uncompressed)

📁 Project Structure

cliss/
├── cliss/
│   └── __init__.py      # CLI, Argument classes
├── pyproject.toml       # Project metadata
├── README.md            # Documentation
└── LICENSE              # MIT License

🔧 Requirements

Dependency	Purpose
Python 3.9+	Type hints, inspect.signature

No external dependencies — stdlib only.

❓ FAQ

Why cliss when argparse already works?

argparse is powerful but verbose. A simple app with 3 commands can easily require 100+ lines of parser setup. cliss reduces this to type-annotated functions — the boilerplate is inferred, not written.

What about Click/Typer/Fire?

Tool	Dependencies	Style
cliss	0 (stdlib)	Decorators + type hints
Click	Click	Decorators
Typer	Click, typing-extensions	Type hints
Fire	0 (stdlib)	Introspection

cliss sits between Fire (zero-config, no validation) and Typer (rich features, heavy deps). It gives you type-driven CLI generation with argparse-compatible control, all in ~200 lines.

Can I use argparse features directly?

Yes. cli.parser and cli.subparsers are standard argparse objects. Add custom actions, mutually exclusive groups, or parent parsers as needed:

cli = CLI(name="myapp")

# Access the underlying argparse parser
group = cli.subparsers.add_parser("admin", help="Admin commands")
admin_sub = group.add_subparsers(dest="admin_command")

@cli.command(name="admin:users")
def list_users(role: str = "all"):
    """List users by role."""
    return f"Listing {role} users"

Does it support nested commands?

For subcommand groups, access cli.subparsers directly or use dotted command names:

@cli.command(name="compute:start")
def start(instance: str):
    return f"Starting {instance}"

@cli.command(name="compute:stop")
def stop(instance: str, force: bool = False):
    action = "Force stopping" if force else "Stopping"
    return f"{action} {instance}"

How does async work?

If the command handler is async def or returns a coroutine, cliss automatically runs it with asyncio.run(). No manual event loop setup needed:

@cli.command()
async def fetch(url: str):
    return f"Fetched {url}"

# Also works with sync functions returning coroutines
@cli.command()
def fetch_sync(url: str):
    async def _fetch():
        return f"Fetched {url}"
    return _fetch()

How does coloured output work?

On Python 3.14+, cliss uses argparse's native color=True for automatic terminal-aware highlighting. On older versions, it falls back to RawDescriptionHelpFormatter for manual ANSI codes. Set colour=False to disable all colours.

🐛 Troubleshooting

Issue	Solution
Arguments not appearing	Check that explicit Argument objects' dest matches parameter names
Bool flag inverted	bool = False → store_true, bool = True → store_false
Type coercion fails	argparse error message shown automatically
Subcommand not found	Verify command name: func.__name__ with _ → - unless overridden
Async handler not awaited	Ensure function is async def or returns a coroutine object
Colours not showing	Requires Python 3.12+ for native colours, or TTY for ANSI fallback. Set colour=False to disable

📄 License

MIT License — see LICENSE file.

🙏 Acknowledgments

• argparse — The foundation this is built on

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Author: Fkernel653 Repository: github.com/Fkernel653/cliss PyPI: pypi.org/project/cliss