Fast API

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints.

Benefits

• Fast: Very high performance, on par with NodeJS and Go.
• Type-checked (catches errors before runtime)
• Automatic API documentation

Anatomy of a FastAPI application

Defines what the API will return (automatic validation!)

Input validation using Pydantic models

Dependency injection (we'll cover this later)

Return values

• FastAPI automatically converts Python dictionaries to JSON
• Content-Type header will be application/json

Path parameters

Synchronous vs Asynchronous in FastAPI

FastAPI supports both synchronous and asynchronous endpoints. Understanding the difference is crucial for building efficient APIs.

Synchronous (Sync) Endpoints

Characteristics:

• Executes code line by line
• Waits for each operation to complete
• Blocks the thread while waiting
• Simpler to understand and debug

Asynchronous (Async) Endpoints

Characteristics:

• Can handle multiple operations concurrently
• Doesn't block while waiting for I/O
• More efficient for I/O-bound operations
• Uses async/await syntax

When to Use Each

Use Sync when:

• Doing CPU-intensive work
• Using libraries that don't support async
• Code is simple and doesn't involve waiting

Use Async when:

• Making HTTP requests
• Database operations (with async driver)
• File I/O operations
• Handling websockets

Common Pitfalls

1. Blocking I/O in Async Functions (Bad)

2. Proper Async Usage (Good)

API Documentation

FastAPI provides automatic interactive API documentation using:

Swagger UI

• Available at /docs
• Interactive documentation
• Try out API endpoints directly
• Shows request/response schemas

ReDoc

• Available at /redoc
• Alternative documentation view
• Better for reading and sharing

How Documentation is Generated

FastAPI uses your:

1. Function names and docstrings
2. Type hints
3. Pydantic models
4. Path operation decorators

Example with full documentation:

This generates:

• Endpoint description
• Request parameters
• Response model
• Example values
• Try it out functionality

Enhancing Documentation

1. Tags - Group endpoints:

2. Summary and Description:

3. Response Description:

4. Status Codes: