Annotated in Python and FastAPI: Deep Dive

Summary

What is Annotated in Python? Annotated is a feature in Python’s type hints system (introduced in Python 3.9 with PEP 593). It allows you to: Define the type of a variable Add extra metadata about how that variable should be handled Python itself ignores this metadata at runtime, but tools (like FastAPI, Pydantic, or linters) can use it. Example from typing import Annotated age: Annotated[int, "must be positive"] Breakdown: int: the core type "must be...