Web Development Basics
FastAPI Introduction
A modern, high-performance web framework for building APIs with Python 3.8+ based on standard Python type hints.
Interview: Modern Python APIs. Crucial for asynchronous API development, validation using Pydantic, and high-concurrency microservices.
FastAPI is a modern, fast (high-performance) web framework for building APIs with Python, based on standard Python type hints. It is built on top of Starlette (for web routing) and Pydantic (for data validation and serialization).
Key Features of FastAPI
- High Performance: On par with NodeJS and Go, thanks to ASGI (Uvicorn) and async architecture.
- Fast Coding: Minimizes boilerplate using standard type hints for validation.
- Automatic Docs: Generates interactive Swagger UI and ReDoc pages automatically from OpenAPI definitions.
- Type Safety: Editor autocomplete and compiler type checks throughout model definitions.
Data Validation with Pydantic
Instead of manually sanitizing user input and returning custom JSON errors for bad inputs, FastAPI validates incoming request payloads against Pydantic models. If the data is invalid, it returns detailed 422 Unprocessable Entity errors automatically.
Use Cases
High-Concurrency APIs — Building microservices that handle high I/O workloads asynchronously.
Machine Learning Service Deployment — Creating interfaces for ML predictions using automatic Pydantic request validation and Swagger documentation.
Serverless functions — Deploying lightweight API gateways that bootstrap quickly.
Common Mistakes
Blocking async threads — Running synchronous database calls inside async def functions, blocking the entire event loop (use def instead of async def for blocking code).
Misunderstanding Pydantic validation vs type hints — Expecting normal type annotations to validate data without inheriting from BaseModel.
Forgetting dependencies injection — Not utilizing FastAPI dependency injection system (Depends) to handle session lifetimes.