Python FastAPI Tutorial: Build a REST API in 2026
Why FastAPI is Python's Best API Framework in 2026
FastAPI has overtaken Flask as the recommended Python web framework for new API projects in 2026. The automatic OpenAPI documentation, Pydantic-based request validation with TypeScript-like type safety, native async/await support, and exceptional performance (comparable to Node.js and Go for I/O-bound workloads) make it the clear choice for Python API development. Django REST Framework remains the choice for full-stack Django projects with complex ORM requirements. Flask is still viable for very simple APIs. FastAPI wins for pure API services.
Project Structure
Organize FastAPI applications with a feature-based structure: routers by domain (users, products, orders), Pydantic schemas separate from database models, dependency injection for shared logic (database sessions, authentication), and a centralized exception handler. The app factory pattern — creating the FastAPI instance in a create_app() function — enables proper testing by creating fresh app instances per test.
Pydantic v2: Request and Response Validation
FastAPI uses Pydantic models for request body validation, response serialization, and query parameter parsing. Pydantic v2 (2023+) is dramatically faster than v1 with a Rust core and improved type support. Define separate schemas for request bodies (CreateUserRequest) and responses (UserResponse) — never expose database model fields like passwords directly. Use model_validator for cross-field validation (e.g., confirming password fields match). Pydantic's ValidationError produces detailed field-level error messages automatically serialized to the API response.
Async Database with SQLAlchemy 2.0
FastAPI's async support pairs with SQLAlchemy 2.0's async engine for non-blocking database queries. Use asyncpg as the PostgreSQL driver for maximum performance. Define database models with SQLAlchemy's declarative base, create async sessions using async_sessionmaker, and inject sessions into route handlers as dependencies. The dependency injection system handles session lifecycle — creating a session per request and closing it after the response, even if an exception occurs.
Authentication with OAuth2 and JWT
FastAPI provides OAuth2PasswordBearer and OAuth2PasswordRequestForm as built-in security utilities. Implement the /token endpoint that validates credentials and returns a JWT, then use Depends(get_current_user) in protected routes to extract and validate the token. FastAPI's dependency injection composes authentication, database sessions, and rate limiting cleanly without middleware spaghetti. The automatic OpenAPI docs include a login form for testing protected endpoints. Download FastAPI project templates at proofmatcher.com.
Originally published at https://proofmatcher.com/blogs/python-fastapi-tutorial-2026