Enhancing Decorators with Type Annotations: Techniques and Best Practices — Koudai Aono

Type hinting can be challenging when working with decorators but is valuable for code quality and maintainability

Python 3.12 introduces new syntax for type annotations in decorators, making it easier to define types without importing TypeVar

ParamSpec can be used for flexible signature handling in decorators, allowing you to capture and preserve function signatures

Protocol classes provide a way to define interfaces for type checking without inheritance, useful for handling different HTTP client libraries

The Callable type with proper annotations helps define function signatures and return types in decorators

Using asterisk (*) in function signatures can enforce keyword arguments in decorators

Type concatenation allows adding or removing specific arguments while maintaining the original type annotations

Response-like protocols can be defined to ensure objects have required methods/attributes (like status_code or json())

Best practices include:

• Using ParamSpec for flexible argument handling
• Leveraging Protocol for interface definitions
• Properly typing return values
• Maintaining original function signatures

Type annotations in decorators improve IDE support and help catch bugs earlier in development