FastAPI vs Flask vs Django comparison

Introduction

These are popular tools to build web apps and APIs. Knowing their differences helps you pick the right one for your project.

You want a simple and lightweight web app or API quickly.

You need automatic data validation and documentation for your API.

You want a full-featured web framework with built-in admin and database tools.

You are building a small project or prototype fast.

You want to handle complex projects with many features and users.

Syntax

FastAPI

FastAPI: from fastapi import FastAPI
app = FastAPI()

Flask: from flask import Flask
app = Flask(__name__)

Django: # Uses project and app structure, not a single code snippet

FastAPI and Flask use simple Python code to create apps.

Django uses a structured project with settings, apps, and models.

Examples

FastAPI example with async function and automatic docs.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello from FastAPI"}

Flask example with simple route and function.

FastAPI

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello from Flask"

Django example with view function and URL routing.

FastAPI

# Django uses views.py and urls.py files
# views.py
from django.http import HttpResponse

def home(request):
    return HttpResponse("Hello from Django")

# urls.py
from django.urls import path
from . import views

urlpatterns = [
    path('', views.home),
]

Sample Program

This FastAPI app responds with a JSON message at the root URL. It uses async function and returns a dictionary that FastAPI converts to JSON automatically.

FastAPI

from fastapi import FastAPI
app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello from FastAPI"}

Important Notes

FastAPI is great for APIs with automatic validation and docs.

Flask is simple and flexible but needs more setup for big projects.

Django is powerful with many built-in features but has more learning curve.

Summary

FastAPI is modern, fast, and good for APIs with type checking.

Flask is minimal and easy to start with for small apps.

Django is full-featured and suits large, complex web apps.

Practice

1. Which framework is best known for being modern, fast, and supporting automatic type checking for APIs?

easy

A. Flask

B. Pyramid

C. Django

D. FastAPI

Solution

1. Step 1: Understand framework features

   FastAPI is designed to be modern and fast, with built-in support for Python type hints to validate and document APIs automatically.

2. Step 2: Compare with other frameworks

   Flask is minimal and easy to start but lacks built-in type checking. Django is full-featured but more heavyweight and not focused on type checking.

3. Final Answer:

   FastAPI -> Option D

4. Quick Check:

   Modern + fast + type checking = FastAPI [OK]

Hint: Modern + fast + type hints = FastAPI [OK]

Common Mistakes:

• Confusing Flask's simplicity with FastAPI's speed
• Thinking Django has built-in type checking
• Choosing Pyramid which is less common

2. Which of the following is the correct way to create a simple route in Flask?

easy

A. app.route('/')(def home(): return 'Hello')

B. @app.route('/')
def home():
return 'Hello'

C. app.get('/')
def home():
return 'Hello'

D. @app.get('/')
def home():
return 'Hello'

Solution

1. Step 1: Recall Flask route syntax

   In Flask, routes are created using the @app.route decorator above a function.

2. Step 2: Identify correct decorator and syntax

   @app.route('/') def home(): return 'Hello' uses @app.route('/') with proper Python function definition and indentation, which is correct Flask syntax.

3. Final Answer:

   @app.route('/') def home(): return 'Hello' -> Option B

4. Quick Check:

   Flask route decorator = @app.route [OK]

Hint: Flask uses @app.route decorator, not app.route() call [OK]

Common Mistakes:

• Missing @ symbol before decorator
• Using app.get instead of app.route in Flask
• Incorrect indentation or function syntax

3. Given this FastAPI code snippet, what will be the output when accessing /items/5?

from fastapi import FastAPI
app = FastAPI()

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    return {'item_id': item_id * 2}

medium

A. {'item_id': 10}

B. {'item_id': '5'}

C. {'item_id': 5}

D. Error: item_id must be a string

Solution

1. Step 1: Understand path parameter and type

   The route expects an integer item_id. When accessing /items/5, item_id is 5 as int.

2. Step 2: Calculate returned value

   The function returns a dictionary with 'item_id' key and value item_id * 2, so 5 * 2 = 10.

3. Final Answer:

   {'item_id': 10} -> Option A

4. Quick Check:

   5 * 2 = 10 output [OK]

Hint: Multiply path param by 2 as int to get output [OK]

Common Mistakes:

• Assuming item_id is string, not int
• Returning original item_id instead of multiplied
• Expecting error due to type mismatch

4. Identify the error in this Django view code snippet:

from django.http import HttpResponse

def home(request):
return HttpResponse('Hello')

medium

A. Indentation error in function body

B. HttpResponse should be replaced with JsonResponse

C. Missing import for HttpRequest

D. Function name must be capitalized

Solution

1. Step 1: Check Python syntax rules

   Python requires the function body to be indented under the def line.

2. Step 2: Identify indentation problem

   The return statement is not indented, causing a syntax error.

3. Final Answer:

   Indentation error in function body -> Option A

4. Quick Check:

   Python function body must be indented [OK]

Hint: Check indentation under def for Python functions [OK]

Common Mistakes:

• Ignoring indentation errors
• Thinking import is missing
• Assuming JsonResponse is mandatory

5. You want to build a large, complex web app with built-in admin, user authentication, and database ORM. Which framework is the best choice and why?

hard

A. FastAPI, because it is the fastest and has built-in admin

B. Flask, because it is minimal and easy to add features manually

C. Django, because it is full-featured with admin, auth, and ORM included

D. FastAPI, because it supports async and type checking

Solution

1. Step 1: Identify requirements for large complex app

   Needs built-in admin panel, user authentication, and ORM for database management.

2. Step 2: Match framework features to requirements

   Django provides all these features out of the box, making it ideal for large apps. FastAPI and Flask require extra setup for these.

3. Final Answer:

   Django, because it is full-featured with admin, auth, and ORM included -> Option C

4. Quick Check:

   Full features for big apps = Django [OK]

Hint: Full features + admin + auth = Django [OK]

Common Mistakes:

• Choosing FastAPI for admin features it lacks
• Thinking Flask has built-in admin
• Ignoring Django's batteries-included approach