Profiling Flask applications - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class from the flask package.

Flask

from flask import [1]
app = [1](__name__)

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

AFlask

BRequest

Crender_template

DBlueprint

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of Flask

Using render_template instead of Flask

Forgetting to import Flask

The Flask class is imported from the flask package to create the app instance.

2fill in blank

medium

Complete the code to add the Flask-Profiler extension to the app.

Flask

from flask_profiler import Profiler

app = Flask(__name__)
app.config["flask_profiler"] = {"enabled": True}
profiler = [1](app)

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

AProfilerApp

BProfilerMiddleware

CProfilerExtension

DProfiler

Attempts:

3 left

💡 Hint

Common Mistakes

Using ProfilerMiddleware which is not part of flask_profiler

Using ProfilerExtension which does not exist

Not passing the app instance

The Profiler class from flask_profiler is used to enable profiling on the Flask app.

3fill in blank

hard

Fix the error in the route decorator to profile the home page.

Flask

@app.route([1])
def home():
    return "Hello, Flask Profiler!"

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

Aapp

B"/"

Chome

D"/home"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name instead of a string path

Using an incorrect path like "home" without slash

Passing the app object instead of a string

The route decorator needs a string path. The home page is at "/".

4fill in blank

hard

Fill both blanks to configure Flask-Profiler to store data in a SQLite database.

Flask

app.config["flask_profiler"] = {
    "enabled": True,
    "storage": [1],
    "storage_path": [2]
}

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

A"sqlite"

B"memory"

C"/tmp/flask_profiler.sqlite"

D"/var/log/flask_profiler"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "memory" storage which does not persist data

Providing a directory path instead of a file path

Not enabling profiling

To store profiling data in SQLite, set storage to "sqlite" and provide a file path for storage_path.

5fill in blank

hard

Fill all three blanks to create a custom middleware that logs request time in Flask.

Flask

import time
from flask import request

@app.before_request
def start_timer():
    [1] = time.time()
    setattr([2], "start_time", [1])

@app.after_request
def log_request(response):
    duration = time.time() - getattr([3], "start_time", time.time())
    print(f"Request took {duration:.4f} seconds")
    return response

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

Astart_time

Brequest

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Not using the request object to store start time

Using inconsistent variable names

Not returning the response in after_request

The middleware saves the start time in the request object and calculates duration after the request.

Practice

1. What is the main purpose of profiling a Flask application?

easy

A. To find slow parts and improve performance

B. To add new routes to the app

C. To change the app's theme

D. To handle user authentication

Solution

1. Step 1: Understand profiling concept

   Profiling is used to measure where the app spends time during execution.

2. Step 2: Identify profiling goal in Flask

   In Flask, profiling helps find slow parts to optimize performance.

3. Final Answer:

   To find slow parts and improve performance -> Option A

4. Quick Check:

   Profiling = Find slow parts [OK]

Hint: Profiling = finding slow parts to speed up app [OK]

Common Mistakes:

• Confusing profiling with adding features
• Thinking profiling changes app design
• Mixing profiling with security tasks

2. Which code snippet correctly adds profiling middleware to a Flask app using Werkzeug?

easy

A. app = ProfilerMiddleware(app, restrictions=[30])

B. from flask_profiler import Profiler
app = Profiler(app)

C. from werkzeug.middleware.profiler import ProfilerMiddleware
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[30])

D. from werkzeug.middleware import Profiler
app = Profiler(app)

Solution

1. Step 1: Import ProfilerMiddleware correctly

   It is imported from werkzeug.middleware.profiler.

2. Step 2: Wrap app.wsgi_app with ProfilerMiddleware

   Correct usage is app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[30]).

3. Final Answer:

   from werkzeug.middleware.profiler import ProfilerMiddleware app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[30]) -> Option C

4. Quick Check:

   Correct import and wrapping = from werkzeug.middleware.profiler import ProfilerMiddleware app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[30]) [OK]

Hint: ProfilerMiddleware wraps app.wsgi_app, not app directly [OK]

Common Mistakes:

• Importing from wrong module
• Wrapping app instead of app.wsgi_app
• Using wrong class names

3. Given this Flask app snippet with profiling enabled, what will be the effect when you run it?

from flask import Flask
from werkzeug.middleware.profiler import ProfilerMiddleware
app = Flask(__name__)
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[10])

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

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

medium

A. The app runs but profiling is disabled silently

B. The app runs normally and prints profiling info for each request in console

C. The app crashes due to wrong middleware usage

D. The app returns profiling data as HTTP response

Solution

1. Step 1: Analyze middleware wrapping

   ProfilerMiddleware wraps app.wsgi_app correctly with restrictions=[10].

2. Step 2: Understand runtime behavior

   App runs normally and profiling info prints to console for each request.

3. Final Answer:

   The app runs normally and prints profiling info for each request in console -> Option B

4. Quick Check:

   Correct middleware = profiling info output [OK]

Hint: ProfilerMiddleware prints profile info to console during requests [OK]

Common Mistakes:

• Expecting profiling data in HTTP response
• Thinking app crashes with middleware
• Assuming profiling is off without errors

4. You added ProfilerMiddleware but see no profiling output. What is the most likely mistake in this code?

from flask import Flask
from werkzeug.middleware.profiler import ProfilerMiddleware
app = Flask(__name__)
app = ProfilerMiddleware(app, restrictions=[10])

@app.route('/')
def index():
    return 'Test'

medium

A. Flask app must be run with debug=True for profiling

B. Missing import of ProfilerMiddleware

C. Restrictions list must be empty

D. ProfilerMiddleware should wrap app.wsgi_app, not app directly

Solution

1. Step 1: Check how ProfilerMiddleware is applied

   It incorrectly wraps app instead of app.wsgi_app.

2. Step 2: Correct usage for profiling

   ProfilerMiddleware must wrap app.wsgi_app to work properly.

3. Final Answer:

   ProfilerMiddleware should wrap app.wsgi_app, not app directly -> Option D

4. Quick Check:

   Wrap app.wsgi_app, not app [OK]

Hint: Always wrap app.wsgi_app with ProfilerMiddleware [OK]

Common Mistakes:

• Wrapping app instead of app.wsgi_app
• Forgetting to import ProfilerMiddleware
• Misconfiguring restrictions parameter

5. You want to profile only the slowest 5 functions in your Flask app and save the results to files in a directory named 'profile'. Which code snippet correctly achieves this?

hard

A. from werkzeug.middleware.profiler import ProfilerMiddleware
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir='./profile')

B. from werkzeug.middleware.profiler import ProfilerMiddleware
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir='.')

C. from werkzeug.middleware.profiler import ProfilerMiddleware
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir='profile.log')

D. from werkzeug.middleware.profiler import ProfilerMiddleware
app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir=None)

Solution

1. Step 1: Understand restrictions parameter

   restrictions=[5] limits output to slowest 5 functions.

2. Step 2: Set profile_dir correctly

   profile_dir must be a directory path, not a file name, to save profile files.

3. Step 3: Choose correct directory path

   './profile' is a directory path suitable for saving logs.

4. Final Answer:

   from werkzeug.middleware.profiler import ProfilerMiddleware app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir='./profile') -> Option A

5. Quick Check:

   restrictions=5 + directory path = from werkzeug.middleware.profiler import ProfilerMiddleware app.wsgi_app = ProfilerMiddleware(app.wsgi_app, restrictions=[5], profile_dir='./profile') [OK]

Hint: profile_dir must be a folder, restrictions limits slowest funcs [OK]

Common Mistakes:

• Using file name instead of directory for profile_dir
• Setting profile_dir to None disables saving
• Misunderstanding restrictions parameter