CAC Core

An API client library providing essential functionality for command-line applications.

This project uses UV for dependency management.

Overview

CAC Core (cac-core) is a Python library that provides common utilities for building robust command-line applications. It includes modules for commands, configuration management, standardized logging, data modeling, and formatted output display.

Features

• CLI Runner: A shared entry point (cac_core.cli.run / make_main) that discovers a package's commands/ tree, builds the nested argparse parser, wires up shell completion, and dispatches — so a CLI tool is just its commands plus a one-line entry point
• Command: Abstract base class with a run()/handle_exception() exit-code template; subclasses implement define_arguments() and execute()
• Shell Completion: Tab-completion of commands, actions, and options via argcomplete, wired automatically by the runner
• Configuration Management: Load/save configs from YAML files with environment variable support, plus ensure_keys() for interactive first-run setup
• Standardized Logging: Consistent, configurable logging across applications
• Data Modeling: Dynamic attribute creation and manipulation with dictionary-like access
• Output Formatting: Display data as tables or JSON with customization options
• Update Checking: Automatically check for package updates from PyPI or GitHub, with configurable intervals and notification options

Installation

pip install cac-core

Usage

Building a CLI application (recommended)

A cac-* tool is just a package with a commands/ tree and a one-line entry point. The shared runner handles discovery, argument parsing, shell completion, and dispatch.

Layout:

myapp/
  __init__.py        # defines `main`
  commands/
    __init__.py
    greet/
      __init__.py
      hello.py       # class GreetHello(Command)

myapp/__init__.py:

from cac_core.cli import make_main

# wire the console-script entry point to this callable:
#   [project.scripts]  myapp = "myapp:main"
main = make_main("myapp", "myapp", "My CLI tool")

myapp/commands/greet/hello.py — the class name must be {Command}{Action} (here GreetHello), and modules whose name starts with _ are treated as private and skipped by discovery:

import cac_core as cac

class GreetHello(cac.command.Command):
    def define_arguments(self, parser):
        self.define_common_arguments(parser)   # adds --output/--verbose
        parser.add_argument("--name", default="World")
        return parser

    def execute(self, args):
        # Return an int exit code (or None for success). Errors may propagate;
        # the base run()/handle_exception template logs them and returns 1.
        print(f"Hello, {args.name}!")
        return 0

That's it — myapp greet hello --name Ada, myapp --help, myapp --verbose greet hello, and tab-completion (see below) all work. Enable completion with eval "$(register-python-argcomplete myapp)" in your shell.

Command (low-level)

You can also drive a Command directly, without the runner:

import cac_core as cac

# Create a command class
class HelloCommand(cac.command.Command):
    def define_arguments(self, parser):
        """Define command arguments"""
        parser.add_argument('--name', default='World',
                          help='Name to greet')

    def execute(self, args):
        """Execute the command with parsed arguments"""
        logger = cac.logger.new(__name__)
        logger.info(f"Hello, {args.name}!")
        return f"Hello, {args.name}!"

# Use the command in your application
if __name__ == "__main__":
    # Create argument parser
    import argparse
    parser = argparse.ArgumentParser(description='Demo application')

    # Initialize command
    cmd = HelloCommand()

    # Add command arguments
    cmd.define_arguments(parser)

    # Parse arguments
    args = parser.parse_args()

    # Execute command
    result = cmd.execute(args)

    # Display result
    print(result)

Configuration

import cac_core as cac

# Load configuration
config = cac.config.Config("myapp")
server_url = config.get("server", "default-value")

# Update configuration
config.set("api_key", "my-secret-key")
config.save()

Logging

import cac_core as cac

# Create a logger
logger = cac.logger.new(__name__)
logger.info("Application started")
logger.debug("Debug information")

Data Models

import cac_core as cac

# Create data model
data = {
    "name": "Project X",
    "status": "active",
    "metadata": {
        "created": "2025-01-01",
        "version": "1.0"
    }
}

model = cac.model.Model(data)
print(model.name)  # "Project X"
print(model.metadata.version)  # "1.0"

Output Formatting

import cac_core as cac

# Create output handler
output = cac.output.Output({"output": "table"})

# Display data as table
models = [model1, model2, model3]
output.print_models(models)

# Display as JSON
output = cac.output.Output({"output": "json"})
output.print_models(models)

Update Checking

import cac_core as cac

# Check for updates to your package (using PyPI by default)
checker = cac.updatechecker.UpdateChecker("your-package-name")
status = checker.check_for_updates()

# Notify users if an update is available
if status["update_available"]:
    print(f"Update available: {status['current_version']} → {status['latest_version']}")

# Convenience function for quick checks
cac.updatechecker.check_package_for_updates("your-package-name", notify=True)

# Configure source options
# PyPI (default)
pypi_checker = cac.updatechecker.UpdateChecker(
    "your-package-name",
    source="pypi"  # This is the default, so it's optional
)

# GitHub
github_checker = cac.updatechecker.UpdateChecker(
    "your-package-name",
    source="github",
    repo="username/repo-name"
)

# Add update checking to your CLI application
def main():
    # Check for updates once per day
    from datetime import timedelta
    checker = cac.updatechecker.UpdateChecker(
        "your-package-name",
        check_interval=timedelta(days=1)
    )

    # Only notify if update is available, otherwise be quiet
    checker.check_for_updates()
    checker.notify_if_update_available(quiet=True)

    # Rest of your application...

Development

pip install uv

# Clone the repository
git clone https://github.com/rpunt/cac_core.git
cd cac_core
uv venv
uv pip install -e .

# Install dependencies
uv pip install -e ".[dev]"
uv pip install -e ".[test]"
uv pip install -e ".[lint]"

# Run tests
uv run pytest

Project Structure

• cli.py - Shared CLI runner (run / make_main): discovery, argument parsing, completion, dispatch
• command.py - Abstract Command base class and exit-code template
• config.py - Configuration management
• logger.py - Standardized logging
• model.py - Data modeling utilities
• output.py - Output formatting
• credentialmanager.py - Cross-platform credential storage
• updatechecker.py - PyPI/GitHub update checks

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.