FastAPI vs Flask vs Django comparison - Performance Comparison

Performance: FastAPI vs Flask vs Django comparison

MEDIUM IMPACT

This comparison affects server response time and initial page load speed by influencing backend processing and API response efficiency.

Choosing a backend framework for fast API response and scalability

FastAPI

from fastapi import FastAPI
app = FastAPI()

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

FastAPI uses async support and modern Python features to handle many requests concurrently without blocking.

📈 Performance Gainnon-blocking async handling reduces response time and improves throughput

Choosing a backend framework for fast API response and scalability

FastAPI

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello from Flask!'

if __name__ == '__main__':
    app.run()

Flask uses synchronous request handling by default, which can block under high load and slow response times.

📉 Performance Costblocks request handling during I/O, increasing response time under concurrency

Performance Comparison

Framework	Concurrency Model	Startup Time	Response Time	Verdict
Flask	Synchronous by default	Fast (~100ms)	Slower under load	[!] OK
Django	Synchronous with async support	Moderate (~200ms)	Moderate	[!] OK
FastAPI	Asynchronous by default	Fast (~120ms)	Fastest under concurrency	[OK] Good

Rendering Pipeline

Backend framework choice affects server processing before HTML or API data reaches the browser, impacting how quickly content can start rendering.

→Server Processing

→Network Transfer

→Browser Rendering

⚠️ BottleneckServer Processing

Core Web Vital Affected

LCP

This comparison affects server response time and initial page load speed by influencing backend processing and API response efficiency.

Optimization Tips

1Use asynchronous frameworks like FastAPI for better concurrency and faster response times.

2Flask is simple but synchronous by default, which can slow down under load.

3Django offers many built-in features but has moderate startup overhead.

Performance Quiz - 3 Questions

Which backend framework generally provides the fastest response times under high concurrency?

A FastAPI

B Flask

C Django

D All perform the same

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and check Time and TTFB (Time To First Byte) for API calls.

What to look for: Lower TTFB and faster response times indicate better backend performance.

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