Building CLI Applications

import argparse
import sys

# Professional CLI with argparse
def create_cli():
    parser = argparse.ArgumentParser(
        description="TaskMaster — A Python Task Manager",
        formatter_class=argparse.RawDescriptionHelpFormatter,
        epilog="""
Examples:
  taskmaster add "Buy groceries" --priority high
  taskmaster list --status pending
  taskmaster done 3
        """
    )
    
    subparsers = parser.add_subparsers(dest="command")
    
    # Add command
    add_p = subparsers.add_parser("add", help="Add a new task")
    add_p.add_argument("title", help="Task title")
    add_p.add_argument("--priority", choices=["low", "medium", "high"], default="medium")
    
    # List command
    list_p = subparsers.add_parser("list", help="List tasks")
    list_p.add_argument("--status", choices=["all", "pending", "done"], default="all")
    
    return parser

# Demo
parser = create_cli()

# Simulated commands
demos = [
    ["add", "Learn Python", "--priority", "high"],
    ["add", "Build portfolio", "--priority", "medium"],
    ["list", "--status", "all"],
]

tasks = []
for demo_args in demos:
    args = parser.parse_args(demo_args)
    if args.command == "add":
        task = {"id": len(tasks) + 1, "title": args.title, "priority": args.priority, "done": False}
        tasks.append(task)
        print(f"✅ Added: {task['title']} [{task['priority']}]")
    elif args.command == "list":
        print("\n📋 Tasks:")
        for t in tasks:
            status = "✅" if t["done"] else "⬜"
            pri = {"high": "🔴", "medium": "🟡", "low": "🟢"}[t["priority"]]
            print(f"  {t['id']}. {status} {pri} {t['title']}")

# Interactive CLI patterns
print("\n=== CLI Best Practices ===")
print("1. Use argparse for complex CLIs")
print("2. Add --help with clear descriptions")
print("3. Use subcommands for multiple actions")
print("4. Support --verbose and --quiet flags")
print("5. Use exit codes (0=success, 1=error)")