duckdantic 1.0.2

Flexible structural typing and runtime validation for Python

Duckdantic 🦆

Duckdantic is a Python library for flexible structural typing and runtime validation. It provides a powerful way to define structural types (traits) and check whether objects satisfy them at runtime, without requiring inheritance or type annotations.

✨ Features

• 🦆 True Duck Typing: Check object structures at runtime without inheritance
• 🏗️ Trait-Based Validation: Define reusable structural requirements
• 🔧 Framework Agnostic: Works with Pydantic, dataclasses, TypedDict, and plain objects
• 🎯 Flexible Policies: Customize type checking behavior to your needs
• 🚀 High Performance: Intelligent caching and optimized field normalization
• 🎨 Intuitive API: Clean, Pythonic interface with excellent IDE support
• 🔌 ABC Integration: Use traits with isinstance() and issubclass()

📦 Installation

pip install duckdantic

For Pydantic support:

pip install "duckdantic[pydantic]"

🚀 Quick Start

Basic Usage

from duckdantic import TraitSpec, FieldSpec, satisfies

# Define a trait
PersonTrait = TraitSpec(
    name="Person",
    fields=(
        FieldSpec("name", str, required=True),
        FieldSpec("age", int, required=True),
    )
)

# Check if objects satisfy the trait
class Employee:
    def __init__(self, name: str, age: int, employee_id: str):
        self.name = name
        self.age = age
        self.employee_id = employee_id

emp = Employee("Alice", 30, "EMP001")
assert satisfies(emp, PersonTrait)  # ✅ True - has required fields

Duck API (Recommended)

The Duck API provides a more ergonomic interface, especially when working with Pydantic models:

from pydantic import BaseModel
from duckdantic import Duck

class User(BaseModel):
    name: str
    email: str
    age: int

class Person(BaseModel):
    name: str
    age: int

# Create a duck type from a Pydantic model
PersonDuck = Duck(Person)

# Check if instances satisfy the duck type
user = User(name="Bob", email="[e-mail]", age=25)
assert isinstance(user, PersonDuck)  # ✅ True - has required fields

# Convert between compatible types
person = PersonDuck.convert(user)  # Creates Person(name="Bob", age=25)

Method Checking

from duckdantic import MethodSpec, methods_satisfy

# Define method requirements
DrawableMethods = [
    MethodSpec("draw", params=[int, int], returns=None),
    MethodSpec("get_color", params=[], returns=str),
]

class Circle:
    def draw(self, x: int, y: int) -> None:
        pass

    def get_color(self) -> str:
        return "red"

assert methods_satisfy(Circle, DrawableMethods)  # ✅ True

ABC Integration

from duckdantic import TraitSpec, FieldSpec, abc_for

# Define a trait
ConfigTrait = TraitSpec(
    name="Config",
    fields=(
        FieldSpec("host", str),
        FieldSpec("port", int),
    )
)

# Create an ABC from the trait
ConfigABC = abc_for(ConfigTrait)

# Use with isinstance
@ConfigABC.register
class ServerConfig:
    host: str = "localhost"
    port: int = 8080

assert isinstance(ServerConfig(), ConfigABC)  # ✅ True

🎯 Use Cases

• API Validation: Ensure objects have required fields before processing
• Plugin Systems: Define interfaces without requiring inheritance
• Type Bridges: Convert between similar types from different libraries
• Testing: Create test doubles that satisfy production interfaces
• Configuration: Validate configuration objects from various sources

📚 Documentation

For comprehensive documentation, visit https://pr1m8.github.io/duckdantic/

• Getting Started Guide
• API Reference
• Examples
• Advanced Usage

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• Inspired by structural typing concepts from TypeScript and Go interfaces
• Built to complement Pydantic's excellent runtime validation
• Thanks to all contributors and users of the library