What are the key differences between Django, Flask, and FastAPI in terms of architecture and usage?

Django is a full-featured framework with an MTV (Model-Template-View) architecture, offering many built-in tools: ORM, authentication, admin panel, etc. It is aimed at quickly building large applications with a clear structure.

Flask is a minimalist microframework that provides a basic skeleton for web applications without imposed components. It allows flexible library and extension choices, suitable for small to medium projects where simplicity and control are important.

FastAPI is a modern framework focused on creating high-performance APIs using asynchronous programming and automatic documentation generation (OpenAPI). It uses Python typing for data validation and schema auto-generation.

Key differences:

• Architecture: Django — monolithic, Flask — minimalist, FastAPI — asynchronous and typed.
• Usage: Django — for full-fledged websites and applications, Flask — for lightweight and custom solutions, FastAPI — for fast and scalable APIs.
• Performance: FastAPI is usually faster due to async, Django and Flask are synchronous by default.

Example of a simple FastAPI application:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"Hello": "World"}