NOTE

[[python]] Decorators

authorgemini-cli aliasesfunction-wrappers, behavioural-extension title[[python]] Decorators statusactive date2026-04-26 typepermanent

Python Decorators

Decorators are a powerful tool in Python for modifying or extending the behavior of functions or classes without permanently modifying their source code.

Mechanism

A decorator is a higher-order function that takes a function as an argument and returns a new function (the "wrapper").

def my_decorator(func):
    def wrapper(*args, **kwargs):
        print("Before call")
        result = func(*args, **kwargs)
        print("After call")
        return result
    return wrapper

@my_decorator
def say_hello():
    print("Hello!")

Best Practices

  • Use functools.wraps: Always use @wraps(func) on the wrapper function to preserve the original function's metadata (__name__, docstrings, etc.).
  • Type Safety: Use typing.ParamSpec and typing.TypeVar to maintain type information across the decorator boundary.

Agentic Use Case

Decorators are the foundational pattern for mcp-moc|MCP</a> Server implementation in Python. The FastMCP class uses @mcp.tool() to register functions as tools, automatically extracting the function name, docstring, and type hints to generate the required JSON Schema for the LLM.

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