Build CLI Apps in Python with Click and Typer: A Practical Guide

import click

@click.command()
@click.option('--name', '-n', default='World', help='Name to greet.')
@click.option('--count', '-c', default=1, help='Number of times to greet.')
def hello(name, count):
    """Simple program that greets NAME for a total of COUNT times."""
    for _ in range(count):
        click.echo(f"Hello {name}!")

if __name__ == '__main__':
    hello()

import click
import os

@click.group()
def cli():
    """File management CLI."""
    pass

@cli.command()
@click.argument('source', type=click.Path(exists=True))
@click.argument('dest', type=click.Path())
@click.option('--force', '-f', is_flag=True, help='Overwrite destination.')
def copy(source, dest, force):
    """Copy file from SOURCE to DEST."""
    if os.path.exists(dest) and not force:
        click.echo('Destination exists. Use --force to overwrite.')
        return
    # Simulate copy
    click.echo(f'Copying {source} to {dest}')

@cli.command()
@click.argument('path', type=click.Path(exists=True))
def info(path):
    """Show file info."""
    stat = os.stat(path)
    click.echo(f'Size: {stat.st_size} bytes')
    click.echo(f'Modified: {stat.st_mtime}')

if __name__ == '__main__':
    cli()

import typer

def main(name: str = typer.Option('World', help='Name to greet.'),
         count: int = typer.Option(1, help='Number of times to greet.')):
    """Simple program that greets NAME for a total of COUNT times."""
    for _ in range(count):
        typer.echo(f"Hello {name}!")

if __name__ == '__main__':
    typer.run(main)

import typer
import os

app = typer.Typer()

@app.command()
def copy(source: str = typer.Argument(..., help='Source file path.'),
         dest: str = typer.Argument(..., help='Destination file path.'),
         force: bool = typer.Option(False, '--force', '-f', help='Overwrite destination.')):
    """Copy file from SOURCE to DEST."""
    if os.path.exists(dest) and not force:
        typer.echo('Destination exists. Use --force to overwrite.')
        raise typer.Exit(1)
    typer.echo(f'Copying {source} to {dest}')

@app.command()
def info(path: str = typer.Argument(..., help='File path.')):
    """Show file info."""
    if not os.path.exists(path):
        typer.echo('File not found.')
        raise typer.Exit(1)
    stat = os.stat(path)
    typer.echo(f'Size: {stat.st_size} bytes')
    typer.echo(f'Modified: {stat.st_mtime}')

if __name__ == '__main__':
    app()

import typer

def main(filename: str = typer.Argument(..., help='File to process.')):
    """Process a file."""
    if not filename.endswith('.txt'):
        typer.echo('Error: Only .txt files are supported.', err=True)
        raise typer.Exit(code=1)
    try:
        with open(filename) as f:
            content = f.read()
    except FileNotFoundError:
        typer.echo(f'Error: File {filename} not found.', err=True)
        raise typer.Exit(code=1)
    except PermissionError:
        typer.echo(f'Error: Permission denied for {filename}.', err=True)
        raise typer.Exit(code=1)
    typer.echo(f'File content: {content[:50]}...')

if __name__ == '__main__':
    typer.run(main)

from click.testing import CliRunner
from hello import hello

def test_hello_default():
    runner = CliRunner()
    result = runner.invoke(hello, [])
    assert result.exit_code == 0
    assert 'Hello World!' in result.output

def test_hello_custom():
    runner = CliRunner()
    result = runner.invoke(hello, ['--name', 'Alice', '--count', '2'])
    assert result.exit_code == 0
    assert result.output == 'Hello Alice!\nHello Alice!\n'

def test_hello_negative_count():
    runner = CliRunner()
    result = runner.invoke(hello, ['--count', '-1'])
    assert result.exit_code == 0  # No validation, but should handle gracefully
    assert 'Hello World!' not in result.output  # No output for negative count

from setuptools import setup, find_packages

setup(
    name='mycli',
    version='0.1.0',
    packages=find_packages(),
    install_requires=[
        'click',
    ],
    entry_points={
        'console_scripts': [
            'mycli=mycli.cli:cli',
        ],
    },
)