Knack CLI Framework

0.13.0 · active · verified Thu Apr 09

Knack is a lightweight Python framework for building command-line interfaces (CLIs) with a focus on ease of use and extensibility. It provides common CLI features like command grouping, argument parsing, help generation, and output formatting. The current version is 0.13.0, with new releases typically tied to Python version support and bug fixes, occurring a few times a year.

Warnings

breaking Knack frequently drops support for older Python versions. Ensure your environment uses a currently supported Python version.
Fix: Upgrade to a supported Python version. For example, v0.13.0 dropped Python 3.8 support; v0.11.0 dropped 3.7; v0.10.0 dropped 3.6. Always check the release notes for the target Knack version for exact Python compatibility.
breaking The internal handling of `bool` default values for arguments changed, which might affect argument parsing logic.
Fix: Prior to v0.11.0, `bool` default values were implicitly converted to `DefaultInt`. This conversion was stopped. If your code relied on this previous, potentially incorrect, behavior for argument default values, verify your argument parsing logic, especially for boolean flags.
gotcha The `colorama` dependency, used for ANSI escape sequences, became conditionally installed only on Windows.
Fix: If your cross-platform project relies on `colorama` being available on non-Windows systems (e.g., for direct import and usage), you will need to explicitly add `colorama` to your project's dependencies for those platforms, as Knack no longer installs it universally.

Install

pip install knack Install stable version

Imports

CLI
```
from knack.cli import CLI
```
CLICommandsLoader
```
from knack.commands import CLICommandsLoader
```
CLICommandsLoader is part of the 'commands' module, not 'cli'.

Quickstart

This quickstart demonstrates how to set up a basic Knack CLI with a single command group and command. It defines a command loader, registers a simple 'hello' command, and then invokes the CLI programmatically. Save this as a Python file and run it directly to see the output.

import sys
from knack.cli import CLI
from knack.commands import CLICommandsLoader

# Define a simple command handler
def hello_command_handler():
    """Says hello."""
    print("Hello from Knack CLI!")
    return 0

# Define a custom commands loader
class MyCommandsLoader(CLICommandsLoader):
    def load_command_table(self, args):
        # Define a command group 'greet' and a command 'hello' within it
        with self.command_group('greet', operations_tmpl='{}#{{}}'.format(__name__)) as g:
            g.command('hello', 'hello_command_handler')
        return self.command_table

# Create the CLI instance
mycli = CLI(cli_name='mycli', commands_loader_cls=MyCommandsLoader)

if __name__ == '__main__':
    # Example of invoking the CLI programmatically.
    # For actual command-line use, you'd typically pass sys.argv[1:].
    # To run this example: python your_script.py
    print("\n--- Invoking 'mycli greet hello' ---")
    exit_code = mycli.invoke(['greet', 'hello'])
    print(f"CLI exited with code: {exit_code}")

    print("\n--- Invoking 'mycli --help' ---")
    exit_code = mycli.invoke(['--help'])
    print(f"CLI exited with code: {exit_code}")

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