Flask vs FastAPI vs Django: Python Web Frameworks

Flask is a minimalist micro-framework, FastAPI is async-first, and Django is batteries-included full-stack — three Python web frameworks compared.

At a Glance

Key Differences

• Performance: FastAPI is significantly faster than Flask and Django for I/O-bound workloads because it’s built on Starlette (ASGI) with native async/await support. FastAPI handles thousands of concurrent connections efficiently. Flask and Django (WSGI) handle one request per thread/worker, requiring more resources for concurrent connections.
• Built-in Features: Django includes an ORM, admin panel, authentication system, forms, serializers, migrations, and a template engine — everything you need for a data-driven web application. Flask gives you a router and a debugger — everything else comes from extensions. FastAPI gives you request validation via Pydantic, auto-generated API docs, and async support — you add your own ORM, auth, and admin.
• API Documentation: FastAPI automatically generates OpenAPI (Swagger) documentation from your type-annotated Python code — no configuration needed. Flask needs Flasgger or Flask-RESTx. Django needs Django REST Framework (DRF) with drf-spectacular or drf-yasg.
• Data Validation: FastAPI uses Pydantic models with automatic request/response validation, serialization, and schema generation. Flask has no built-in validation (use Marshmallow or Pydantic). Django has form/model validation and DRF adds serializers.

When to Choose Flask

Choose Flask for small to medium projects where you want minimal overhead and maximum flexibility. Flask is excellent for microservices, simple APIs, and web applications where you want to choose your own tools. Flask’s simplicity makes it ideal for learning web development — the entire framework is small enough to understand fully. Flask is also great for integrating with existing databases or services where Django’s ORM would be overkill.

When to Choose FastAPI

Choose FastAPI when you need high-performance async APIs, real-time features (WebSockets), or automatic API documentation. FastAPI is the best choice for building modern REST or GraphQL APIs, especially for data science and ML model serving. FastAPI’s async support makes it ideal for I/O-heavy workloads — calling external APIs, querying databases, processing file uploads. FastAPI’s dependency injection system makes testing and authentication clean. At DodaTech, FastAPI powers the real-time threat detection API for Durga Antivirus Pro.

When to Choose Django

Choose Django for large, data-intensive web applications where “batteries included” matters. Django’s built-in admin panel can save months of development for CRUD applications. Django’s ORM is the most mature Python ORM with excellent migration support. Django follows “Convention over Configuration” — the framework makes decisions for you so your team can focus on business logic. Django is the best choice for content management systems, e-commerce platforms, and social media applications.

Side by Side Code Example: Simple API Endpoint

Flask

from flask import Flask, jsonify, request

app = Flask(__name__)

@app.route("/items/<int:item_id>")
def get_item(item_id):
    item = {"id": item_id, "name": "Widget"}
    return jsonify(item)

@app.route("/items", methods=["POST"])
def create_item():
    data = request.get_json()
    return jsonify(data), 201

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    id: int
    name: str

@app.get("/items/{item_id}")
def get_item(item_id: int):
    return {"id": item_id, "name": "Widget"}

@app.post("/items", status_code=201)
def create_item(item: Item):
    return item

Django (using DRF)

from rest_framework import generics
from .models import Item
from .serializers import ItemSerializer

class ItemDetail(generics.RetrieveAPIView):
    queryset = Item.objects.all()
    serializer_class = ItemSerializer

class ItemCreate(generics.CreateAPIView):
    queryset = Item.objects.all()
    serializer_class = ItemSerializer

FastAPI’s code is closest to plain Python — type annotations define the schema. Flask requires manual JSON parsing and response building. Django with DRF uses class-based views and serializers. FastAPI automatically generates OpenAPI docs; Flask and Django require extensions.

FAQ