FastAPI vs Django vs Flask

Python has three major web frameworks: Django (batteries included), Flask (minimalist), and now FastAPI (modern async). Each has its place.

The Quick Summary

FastAPI: The New Kid

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class User(BaseModel):
    name: str
    email: str

@app.get("/users/{user_id}")
async def get_user(user_id: int) -> User:
    return User(name="Alice", email="alice@example.com")

@app.post("/users/")
async def create_user(user: User) -> User:
    return user

Run with: uvicorn main:app --reload

Standout features:

• Automatic OpenAPI docs at /docs
• Pydantic for validation
• Async by default
• Type hints drive the API

Django: The Full Package

# models.py
from django.db import models

class User(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField()

# views.py
from rest_framework import viewsets
from .models import User
from .serializers import UserSerializer

class UserViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()
    serializer_class = UserSerializer

# urls.py
from rest_framework.routers import DefaultRouter
router = DefaultRouter()
router.register('users', UserViewSet)

Standout features:

• Admin panel for free
• ORM with migrations
• Authentication built-in
• Massive ecosystem

Flask: The Minimalist

from flask import Flask, jsonify, request

app = Flask(__name__)

users = {}

@app.route('/users/<int:user_id>')
def get_user(user_id):
    return jsonify(users.get(user_id, {}))

@app.route('/users/', methods=['POST'])
def create_user():
    data = request.get_json()
    users[len(users)] = data
    return jsonify(data), 201

Standout features:

• Learn in an afternoon
• Choose your own components
• Excellent for microservices
• No magic

Performance Comparison

Benchmarks vary, but the pattern is consistent:

FastAPI’s ASGI + async gives it a real edge for I/O-bound workloads.

When to Choose Each

Choose Django When

• Building a full web application (not just API)
• Need admin interface
• Want ORM with migrations
• Security is critical (built-in protections)
• Team knows Django

# Django gives you this for free
# - User authentication
# - Admin panel
# - CSRF protection
# - ORM + migrations
# - Template engine

Choose Flask When

• Building microservices
• Learning web development
• Need maximum flexibility
• Simple API with custom components
• Existing Flask codebase

# Flask: add what you need
from flask_sqlalchemy import SQLAlchemy
from flask_login import LoginManager
from flask_marshmallow import Marshmallow

Choose FastAPI When

• Building pure APIs
• Performance matters
• Team knows type hints
• Want auto-generated docs
• Async is important

# FastAPI: types drive everything
from fastapi import FastAPI, Query

@app.get("/items/")
async def list_items(
    skip: int = Query(default=0, ge=0),
    limit: int = Query(default=10, le=100)
):
    return items[skip : skip + limit]

Hybrid Approaches

FastAPI with SQL

from fastapi import FastAPI, Depends
from sqlalchemy.orm import Session
from . import models, database

app = FastAPI()

def get_db():
    db = database.SessionLocal()
    try:
        yield db
    finally:
        db.close()

@app.get("/users/{user_id}")
def get_user(user_id: int, db: Session = Depends(get_db)):
    return db.query(models.User).filter(models.User.id == user_id).first()

Django Ninja

FastAPI-style APIs in Django:

from ninja import NinjaAPI
from .models import User

api = NinjaAPI()

@api.get("/users/{user_id}")
def get_user(request, user_id: int):
    return User.objects.get(id=user_id)

Best of both: Django’s ORM + FastAPI’s ergonomics.

Migration Considerations

Flask → FastAPI

Relatively straightforward:

• Route decorators are similar
• Add type hints
• Switch to async where beneficial
• Replace validation with Pydantic

Django → FastAPI

Harder:

• Lose the ORM (or use SQLAlchemy)
• Lose the admin
• Lose the ecosystem
• Only worth it for API-only projects

My Recommendations

Starting a new project?

• Full web app: Django
• Pure API: FastAPI
• Learning: Flask

Existing project?

• Stay with what you have
• Django Ninja for Django + FastAPI benefits

Microservices?

• FastAPI or Flask
• Django is overkill

Final Thoughts

There’s no “best” framework. Django, Flask, and FastAPI solve different problems.

Django: “I don’t want to think about components” Flask: “I want to choose my own adventure” FastAPI: “I want modern async with type safety”

Choose based on your project needs, team skills, and personal preference. They’re all production-ready.

The best framework is the one that ships your product.