Flask-Limiter for rate limiting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask-Limiter extension.

Flask

from flask_limiter import [1]

Drag options to blanks, or click blank then click option'

ALimiter

BLimiterExtension

CRateLimiter

DLimiterTool

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect class names like 'RateLimiter' or 'LimiterExtension'.

Trying to import from 'flask_limiter_extension' instead of 'flask_limiter'.

The Flask-Limiter extension is imported using Limiter.

2fill in blank

medium

Complete the code to create a Flask app and initialize Limiter with a default rate limit of 5 per minute.

Flask

app = Flask(__name__)
limiter = Limiter(app, default_limits=["[1]"])

Drag options to blanks, or click blank then click option'

A5 per minute

B10 per second

C100 per hour

D1 per day

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers without quotes.

Using wrong time units like 'per seconds' instead of 'per second'.

The default rate limit is set as a string like '5 per minute' to limit requests to 5 each minute.

3fill in blank

hard

Fix the error in the route decorator to apply a rate limit of 3 per minute.

Flask

@app.route("/")
@limiter.limit("[1]")
def home():
    return "Hello!"

Drag options to blanks, or click blank then click option'

A3 per second

B3 per hour

C3 per day

D3 per minute

Attempts:

3 left

💡 Hint

Common Mistakes

Using '3 per seconds' which is grammatically incorrect.

Using '3 per hour' which is a different rate.

The rate limit string must be '3 per minute' to limit to 3 requests each minute.

4fill in blank

hard

Fill both blanks to create a rate limit key function that limits by remote address.

Flask

limiter = Limiter(app, key_func=[1], default_limits=["10 per minute"])

@app.route("/data")
@limiter.limit("5 per minute", key_func=[2])
def data():
    return "Data"

Drag options to blanks, or click blank then click option'

Aget_remote_address

Bremote_addr

Cclient_ip

Duser_ip

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names like 'remote_addr' instead of the function.

Using made-up names like 'client_ip' or 'user_ip'.

The function get_remote_address is used by Flask-Limiter to get the client's IP address for rate limiting.

5fill in blank

hard

Fill all three blanks to create a custom error message for rate limit exceeded.

Flask

from flask import Flask, jsonify
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address

app = Flask(__name__)
limiter = Limiter(app, key_func=get_remote_address, default_limits=["5 per minute"])

@app.errorhandler([1])
def ratelimit_handler(e):
    return jsonify(error="[2]"), [3]

Drag options to blanks, or click blank then click option'

A429

BRate limit exceeded. Try again later.

C429 Too Many Requests

D403

Attempts:

3 left

💡 Hint

Common Mistakes

Using 403 Forbidden instead of 429.

Returning a status code as a string instead of an integer.

The HTTP status code for rate limit exceeded is 429. The error message is a friendly string. The handler returns status code 429.

Practice

1. What is the main purpose of using Flask-Limiter in a Flask application?

easy

A. To limit how many requests a user can make in a given time

B. To speed up the Flask application by caching responses

C. To automatically generate API documentation

D. To handle database migrations smoothly

Solution

1. Step 1: Understand Flask-Limiter's role

   Flask-Limiter is designed to control the number of requests a user can make to prevent abuse.

2. Step 2: Compare options with Flask-Limiter's purpose

   Options A, B, and D relate to documentation, caching, and migrations, which are unrelated to rate limiting.

3. Final Answer:

   To limit how many requests a user can make in a given time -> Option A

4. Quick Check:

   Flask-Limiter = request limiting [OK]

Hint: Flask-Limiter controls request frequency to protect your app [OK]

Common Mistakes:

• Confusing Flask-Limiter with caching tools
• Thinking it manages database or docs
• Assuming it speeds up the app

2. Which of the following is the correct way to apply a rate limit of 5 requests per minute to a Flask route using Flask-Limiter?

easy

A. @limiter.limit('minute/5')\ndef my_route():\n return 'Hello'

B. @limiter.limit(5)\ndef my_route():\n return 'Hello'

C. @limiter.limit('5 requests')\ndef my_route():\n return 'Hello'

D. @limiter.limit('5/minute')\ndef my_route():\n return 'Hello'

Solution

1. Step 1: Check the syntax for rate limit string

   The correct format is a string like '5/minute' specifying count and time unit.

2. Step 2: Validate each option's syntax

   @limiter.limit('5/minute')\ndef my_route():\n return 'Hello' uses '5/minute' which is correct. Options B, C, and D use incorrect formats or missing quotes.

3. Final Answer:

   @limiter.limit('5/minute')\ndef my_route():\n return 'Hello' -> Option D

4. Quick Check:

   Correct limit string format = @limiter.limit('5/minute')\ndef my_route():\n return 'Hello' [OK]

Hint: Use string 'count/unit' like '5/minute' in @limiter.limit [OK]

Common Mistakes:

• Omitting quotes around the limit string
• Using numbers without units
• Incorrect time unit format

3. Given this Flask app snippet using Flask-Limiter:

from flask import Flask
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address

app = Flask(__name__)
limiter = Limiter(app, key_func=get_remote_address)

@app.route('/')
@limiter.limit('2/minute')
def home():
    return 'Welcome!'

# Assume the same client makes 3 quick requests

What will happen on the third request from the same client within one minute?

medium

A. The third request will be blocked with a 429 Too Many Requests error

B. The third request will succeed and return 'Welcome!'

C. The app will crash with an exception

D. The third request will be delayed but eventually succeed

Solution

1. Step 1: Understand the limit set

   The route is limited to 2 requests per minute per client IP.

2. Step 2: Analyze the third request behavior

   The third request exceeds the limit, so Flask-Limiter blocks it with a 429 error.

3. Final Answer:

   The third request will be blocked with a 429 Too Many Requests error -> Option A

4. Quick Check:

   Requests > limit = 429 error [OK]

Hint: Requests over limit get 429 error response [OK]

Common Mistakes:

• Thinking extra requests succeed silently
• Assuming app crashes on limit exceed
• Believing requests get delayed instead of blocked

4. Consider this Flask app code snippet using Flask-Limiter:

from flask import Flask
from flask_limiter import Limiter

app = Flask(__name__)
limiter = Limiter(app)

@app.route('/test')
@limiter.limit('3/minute')
def test():
    return 'Test'

When running this code, the rate limiting does not work as expected. What is the most likely cause?

medium

A. The limit string '3/minute' is invalid syntax

B. The decorator @limiter.limit must be placed before @app.route

C. Missing key_func argument to identify clients, so all requests share the same limit

D. Flask-Limiter requires Flask app to be created after Limiter

Solution

1. Step 1: Check Limiter initialization

   Limiter is created without a key_func, so it uses default which may not distinguish clients properly.

2. Step 2: Understand key_func role

   Without key_func like get_remote_address, all requests share the same limit, causing unexpected behavior.

3. Final Answer:

   Missing key_func argument to identify clients, so all requests share the same limit -> Option C

4. Quick Check:

   key_func missing = shared limit problem [OK]

Hint: Always set key_func to identify clients for correct limits [OK]

Common Mistakes:

• Assuming limit string syntax is wrong
• Thinking decorator order matters here
• Believing app creation order affects Limiter

5. You want to apply a global rate limit of 10 requests per minute for all routes but allow a specific route /special to have a higher limit of 30 requests per minute using Flask-Limiter. Which code snippet correctly implements this?

hard

A. limiter = Limiter(app)

@app.route('/special')
@limiter.limit('30/minute')
def special():
return 'Special access'

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

B. limiter = Limiter(app, key_func=get_remote_address, default_limits=['10/minute'])

@app.route('/special')
@limiter.limit('30/minute')
def special():
return 'Special access'

C. limiter = Limiter(app, key_func=get_remote_address, default_limits=['30/minute'])

@app.route('/special')
@limiter.limit('10/minute')
def special():
return 'Special access'

D. limiter = Limiter(app, key_func=get_remote_address)

@app.route('/special')
@limiter.limit('10/minute')
def special():
return 'Special access'

limiter.default_limits = ['30/minute']

Solution

1. Step 1: Set global default limits

   Use default_limits=['10/minute'] in Limiter to apply global rate limits.

2. Step 2: Override limit on specific route

   Use @limiter.limit('30/minute') decorator on /special route to allow higher limit.

3. Final Answer:

   limiter = Limiter(app, key_func=get_remote_address, default_limits=['10/minute']) @app.route('/special') @limiter.limit('30/minute') def special(): return 'Special access' -> Option B

4. Quick Check:

   Global default + route override = limiter = Limiter(app, key_func=get_remote_address, default_limits=['10/minute']) @app.route('/special') @limiter.limit('30/minute') def special(): return 'Special access' [OK]

Hint: Set default_limits globally, override with @limiter.limit per route [OK]

Common Mistakes:

• Confusing default_limits with per-route limits
• Not setting key_func for client identification
• Trying to change default_limits after initialization