typer-patterns

Provides modern type-safe Typer CLI patterns including type hints, Enum usage, sub-app composition, and Typer() instance patterns for building maintainable command-line applications.

Core Patterns

1. Type-Safe Commands with Type Hints

Use Python type hints for automatic validation and better IDE support:

import typer
from typing import Optional
from pathlib import Path

app = typer.Typer()

@app.command()
def process(
    input_file: Path = typer.Argument(..., help="Input file path"),
    output: Optional[Path] = typer.Option(None, help="Output file path"),
    verbose: bool = typer.Option(False, "--verbose", "-v"),
    count: int = typer.Option(10, help="Number of items to process")
) -> None:
    """Process files with type-safe parameters."""
    if verbose:
        typer.echo(f"Processing {input_file}")

2. Enum-Based Options

Use Enums for constrained choices with autocomplete:

from enum import Enum

class OutputFormat(str, Enum):
    json = "json"
    yaml = "yaml"
    text = "text"

@app.command()
def export(
    format: OutputFormat = typer.Option(OutputFormat.json, help="Output format")
) -> None:
    """Export with enum-based format selection."""
    typer.echo(f"Exporting as {format.value}")

3. Sub-Application Composition

Organize complex CLIs with sub-apps:

app = typer.Typer()
db_app = typer.Typer()
app.add_typer(db_app, name="db", help="Database commands")

@db_app.command("migrate")
def db_migrate() -> None:
    """Run database migrations."""
    pass

@db_app.command("seed")
def db_seed() -> None:
    """Seed database with test data."""
    pass

4. Typer() Instance Pattern

Use Typer() instances for better organization and testing:

def create_app() -> typer.Typer:
    """Factory function for creating Typer app."""
    app = typer.Typer(
        name="myapp",
        help="My CLI application",
        add_completion=True,
        no_args_is_help=True
    )

    @app.command()
    def hello(name: str) -> None:
        typer.echo(f"Hello {name}")

    return app

app = create_app()

if __name__ == "__main__":
    app()

Usage Workflow

1. Identify pattern need: Determine which Typer pattern fits your use case
2. Select template: Choose from templates/ based on complexity
3. Customize: Adapt type hints, Enums, and sub-apps to your domain
4. Validate: Run validation script to check type safety
5. Test: Use example tests as reference

Template Selection Guide

• basic-typed-command.py: Single command with type hints
• enum-options.py: Commands with Enum-based options
• sub-app-structure.py: Multi-command CLI with sub-apps
• typer-instance.py: Factory pattern for testable CLIs
• advanced-validation.py: Custom validators and callbacks

Validation

Run the type safety validation:

./scripts/validate-types.sh path/to/cli.py

Checks:

• All parameters have type hints
• Return types specified
• Enums used for constrained choices
• Proper Typer decorators

Examples

See examples/ for complete working CLIs:

• examples/basic-cli/: Simple typed CLI
• examples/enum-cli/: Enum-based options
• examples/subapp-cli/: Multi-command with sub-apps
• examples/factory-cli/: Testable Typer factory pattern

Best Practices

1. Always use type hints: Enables auto-validation and IDE support
2. Prefer Enums over strings: For constrained choices
3. Use Path for file paths: Better validation than str
4. Document with docstrings: Typer uses them for help text
5. Keep commands focused: One command = one responsibility
6. Use sub-apps for grouping: Organize related commands together
7. Test with factory pattern: Makes CLIs unit-testable

Common Patterns

Callback for Global Options

@app.callback()
def main(
    verbose: bool = typer.Option(False, "--verbose", "-v"),
    ctx: typer.Context = typer.Context
) -> None:
    """Global options applied to all commands."""
    ctx.obj = {"verbose": verbose}

Custom Validators

def validate_port(value: int) -> int:
    if not 1024 <= value <= 65535:
        raise typer.BadParameter("Port must be between 1024-65535")
    return value

@app.command()
def serve(port: int = typer.Option(8000, callback=validate_port)) -> None:
    """Serve with validated port."""
    pass

Rich Output Integration

from rich.console import Console

console = Console()

@app.command()
def status() -> None:
    """Show status with rich formatting."""
    console.print("[bold green]System online[/bold green]")

Integration Points

• Use with cli-structure skill for overall CLI architecture
• Combine with testing-patterns for CLI test coverage
• Integrate with packaging skill for distribution

References

• Templates: templates/
• Scripts: scripts/validate-types.sh, scripts/generate-cli.sh
• Examples: examples/*/