Flask Interview Questions

Introduction

Flask is a popular Python web framework used for building web applications. It's known for being lightweight, flexible & easy to learn, making it a great choice for beginners & experienced developers alike. Flask allows you to quickly create web apps by providing the basic and important features needed, without being worrying about project structure or design choices.

In this article, we'll cover some common Flask interview questions to help you prepare for your next interview or expand your understanding of the framework.

Beginner-Level Flask Interview Questions and Answers

1. What is the difference between Flask & Django?

Flask & Django are both Python web frameworks but have some key differences:

Flask is a microframework, providing only the essentials for web development. It's lightweight, flexible & easy to learn. Flask allows the developer to choose what libraries & tools to use.

Django is a full-stack framework that includes many built-in features like an admin panel, ORM, authentication & more. It's opinionated & has a steeper learning curve but can be great for large, complex projects.

2. Why do we use Flask(name) in Flask?

In Flask, the Flask(__name__) line creates an instance of the Flask class. The name argument tells Flask where to look for templates, static files & so on. It's a special Python variable that holds the name of the current module. Passing name allows Flask to determine if the current module is being run directly or being imported, which helps it locate resources properly.

3. What is routing in Flask?

In Flask, routing refers to mapping URLs to view functions that handle requests. You define routes using the @app.route() decorator, specifying the URL path as an argument. Here's an example:

@app.route('/')
def home():
    return 'Welcome to the homepage!'
@app.route('/about')
def about():
    return 'This is the about page.'

When a user visits the root URL ('/'), Flask calls the home() function & returns the message. Similarly, visiting '/about' triggers the about() function.

4. Describe Flask error handlers.

Flask allows you to define custom error handlers for HTTP error codes. Here's an example:

@app.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

This defines a custom handler for 404 errors. When a 404 error occurs, Flask will call the page_not_found function & return the specified message & error code. You can define handlers for various error codes like 500, 403, etc.

5. Explain the use of context processors in Flask.

Context processors in Flask allow you to make variables globally available to all templates without explicitly passing them in every render_template() call. They are functions that return a dictionary of variables to be added to the template context. Here's an example:

@app.context_processor
def inject_user():
    return dict(user=g.user)

This context processor makes the user variable from Flask's g object available in all templates. You can then use {{ user }} in any template to access the current user.

6. Why is Flask called a microframework?

Flask is called a microframework because it aims to keep the core of the framework simple & extensible. Flask provides only the essentials needed for web development, such as routing, templating & request handling. It doesn't include built-in components for database abstraction, form validation, authentication & so on. This minimalistic approach allows developers to choose the libraries they want based on project needs. Flask's simplicity & flexibility make it easy to understand & customize, which is why it's called a microframework.

7. What HTTP methods does Python Flask provide?

Flask provides decorators for common HTTP methods:

@app.route(methods=['GET']) for GET requests (default)
@app.route(methods=['POST']) for POST requests
@app.route(methods=['PUT']) for PUT requests
@app.route(methods=['DELETE']) for DELETE requests
@app.route(methods=['PATCH']) for PATCH requests

You can specify multiple methods in the list to handle different request types for the same route.

8. How can you make a Flask app asynchronous?

To make a Flask app asynchronous, you can use extensions like Flask-SocketIO or Flask-AsyncIO that integrate asynchronous frameworks with Flask. Here's an example using Flask-SocketIO:

from flask_socketio import SocketIO, emit
socketio = SocketIO(app)
@socketio.on('message')
def handle_message(message):
    emit('response', {'data': 'Received: ' + message})
if __name__ == '__main__':
    socketio.run(app)

This sets up a WebSocket connection using SocketIO. The @socketio.on decorator defines an event handler for incoming 'message' events. The emit() function sends a 'response' event back to the client.

9. In Flask, what do you mean by template engines?

Template engines in Flask allow you to dynamically generate HTML pages by inserting Python variables & expressions into HTML templates. Flask uses the Jinja2 template engine by default. Templates contain static parts of the page & placeholders for dynamic content.

Here's an example template:

<h1>Hello, {{ name }}!</h1>
<p>Welcome to my website.</p>

The {{ name }} is a placeholder that will be replaced with the value of the name variable passed from the Flask view function.

10. What is Flask-Migrate?

Flask-Migrate is an extension for Flask that facilitates SQLAlchemy database migrations using Alembic. It helps manage database schema changes by creating migration scripts, which can be applied or rolled back as needed. This ensures consistent database structure across different environments, making it easier to maintain and update the database schema in Flask applications.

Intermediate Level Flask Interview Questions and Answers

11. What is Flask-WTF & what are its characteristics?

Flask-WTF is an extension that simplifies handling web forms in Flask. Its key features include:

Integration with WTForms for form rendering & validation

CSRF (Cross-Site Request Forgery) protection
reCAPTCHA support
File upload handling

Here's an example of creating a form with Flask-WTF:

from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired
class NameForm(FlaskForm):
    name = StringField('Name', validators=[DataRequired()])
    submit = SubmitField('Submit')

This defines a form with a name field & submit button. The DataRequired validator ensures the field isn't submitted empty.

12. What is Flask-Migrate & how do you use it?

Flask-Migrate is an extension that handles SQLAlchemy database migrations for Flask applications. It's built on top of Alembic, a database migration framework. With Flask-Migrate, you can:

Create migration scripts to modify your database schema
Apply or revert migrations
Automate the migration process

Here's a basic example of using Flask-Migrate:

from flask_migrate import Migrate
migrate = Migrate(app, db)
# Generate a migration script
flask db migrate -m "Initial migration"
# Apply the migration to the database 
flask db upgrade

This creates a migration script based on changes to your SQLAlchemy models & applies it to update the database schema.

13. What is the g object in Flask? What distinguishes it from the session object?

The g object in Flask is a global namespace for holding data during a single request. It's useful for storing resources that need to be accessed by multiple functions during a request.

The key differences between g & session are:

g is specific to each request & not persisted across requests
session persists data across requests in a cookie or server-side storage
g is accessible only within the context of a request, while the session is available across requests

Here's an example of using g:

from flask import g
@app.before_request
def set_user():
    g.user = 'John'
@app.route('/user')
def get_user():
    return f"User: {g.user}"

The @app.before_request decorator sets the g.user variable before each request. The /user route can then access g.user to return the user's name.

14. Mention how you can enable debugging in Flask.

To enable debugging in Flask, you can set the debug parameter to True when running the app:

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

When debug mode is enabled:

Flask will display detailed error messages in the browser
The app will automatically reload whenever the code changes
An interactive debugger will be available in the browser when an exception occurs

Note: Debugging should only be enabled during development, not in production, as it can expose sensitive information.

15. How to create a RESTful application in Flask?

To create a RESTful application in Flask, you can use the Flask-RESTful extension. It provides a simple way to define resource classes & map them to URLs. Here's a basic example:

from flask import Flask
from flask_restful import Api, Resource
app = Flask(__name__)
api = Api(app)
class HelloWorld(Resource):
    def get(self):
        return {'hello': 'world'}
api.add_resource(HelloWorld, '/')
if __name__ == '__main__':
    app.run()

In this example:

We import the necessary classes from flask_restful
Create an instance of the Api class, passing the Flask app
Define a resource class HelloWorld with a get method that returns a dictionary
Map the resource to the root URL using api.add_resource()

Flask-RESTful handles content negotiation, request parsing & response formatting for you.

16. What is Flask-Sijax?

Flask-Sijax is an extension that integrates Sijax (Simple Ajax) with Flask. Sijax is a Python/jQuery library that simplifies AJAX interactions between the client & server. Flask-Sijax allows you to define Python functions that can be called from JavaScript using AJAX. Here's a simple example:

from flask import Flask, g
from flask_sijax import sijax
app = Flask(__name__)
@app.route('/')
@sijax.route(app, default_request_uri='/')
def index():
    def hello(obj_response):
        obj_response.alert('Hello, world!')       
    if g.sijax.is_sijax_request:
        g.sijax.register_callback('hello', hello)
        return g.sijax.process_request()   
    return '''
        <script>
            function sayHello() {
                Sijax.request('hello');
            }
        </script>
        <button onclick="sayHello()">Say Hello</button>
    '''
if __name__ == '__main__':
    app.run()

In this example:

The @sijax.route decorator is used to enable Sijax on the route
The hello function is defined to be called from JavaScript
g.sijax.is_sijax_request checks if the current request is a Sijax request
If it is, the hello function is registered as a Sijax callback & the request is processed
The returned HTML includes a button that triggers the sayHello JavaScript function, which calls the hello Python function using Sijax

Flask-Sijax simplifies AJAX communication between the client & server in this way.

17. How to get a visitor's IP address in Flask?

You can get a visitor's IP address in Flask using the request object. Here's an example:

from flask import request
@app.route('/')
def index():
    ip_address = request.remote_addr
    return f'Your IP address is: {ip_address}'

In this code:

The request object is imported from Flask
The remote_addr attribute of the request object holds the IP address of the client making the request
The IP address is returned in the response

Note that if your app is behind a proxy server, you might need to use request.headers.get('X-Forwarded-For') instead to get the correct client IP address.

18. Explain application context & request context in Flask.

In Flask, there are two main types of contexts: application context & request context.

The application context keeps track of application-level data, such as configuration settings, database connections & logger objects. It allows Flask extensions to access the current application instance using the current_app variable.
The request context, on the other hand, keeps track of data specific to the current request, such as request arguments, form data, session variables & g object. It allows access to request-specific information using the request & session variables.

Both contexts work as stacks, meaning they can be pushed & popped as needed. When a request comes in, Flask pushes a request context, which also pushes an application context if one isn't already active. When the request is completed, Flask pops the request context, & the application context if it was pushed by the request.

Here's an example demonstrating the usage of application & request contexts:

from flask import current_app, request
@app.route('/')
def index():
    # Accessing application context
    app_name = current_app.name
    
    # Accessing request context
    request_method = request.method

    return f'Application: {app_name}, Request Method: {request_method}'

In this code:

current_app.name accesses the name of the current application instance from the application context
request.method accesses the HTTP method of the current request from the request context

Understanding the difference between application & request contexts is important for managing data & resources in Flask applications.

19. How do you handle API versioning in Flask?

There are a few common approaches to handle API versioning in Flask:

a. URL Versioning:

Include the version number in the URL. For example:

@app.route('/api/v1/users')
def get_users_v1():
    # ...
@app.route('/api/v2/users')
def get_users_v2():
    # ...

b. Accept Header Versioning:

Use the Accept header to specify the API version. For example:

@app.route('/users')
def get_users():
    version = request.headers.get('Accept', '').split('version=')[-1]
    if version == 'v1':
        # Return response for v1
    elif version == 'v2':
        # Return response for v2
    else:
        # Handle unsupported version

c. Versioned Blueprints:

Use Flask blueprints to create separate versioned modules. For example:

from flask import Blueprint
v1_blueprint = Blueprint('v1', __name__, url_prefix='/v1')
v2_blueprint = Blueprint('v2', __name__, url_prefix='/v2')
@v1_blueprint.route('/users')
def get_users_v1():
    # ...
@v2_blueprint.route('/users')  
def get_users_v2():
    # ...
app.register_blueprint(v1_blueprint)
app.register_blueprint(v2_blueprint)

d. Versioned Namespaces with Flask-RESTful:

If you're using Flask-RESTful, you can define versioned namespaces. For example:

from flask_restful import Api
api = Api(app)
class UsersV1(Resource):
    def get(self):
        # ...
class UsersV2(Resource):  
    def get(self):
        # ...
api.add_resource(UsersV1, '/v1/users')
api.add_resource(UsersV2, '/v2/users')

Choose the approach that best fits your API design & requirements. Ensure that you document the versioning scheme clearly for API consumers.

20. Explain how you can access sessions in Flask.

Flask provides a session object to handle sessions. Sessions allow you to store data specific to each user across requests. Here's how to use sessions:

from flask import session
@app.route('/set')
def set_session():
    session['username'] = 'John'
    return 'Session set'
@app.route('/get')
def get_session():
    username = session.get('username')
    return f"Username: {username}"

In this example, the set_session route sets a 'username' key in the session. The get_session route retrieves the 'username' from the session using session.get().

Remember to set a secret key for your app to enable sessions:

app.secret_key = 'your-secret-key'

Advanced Level Flask Interview Questions and Answers

21. Explain how to deploy a Flask application using Docker.

To deploy a Flask application using Docker, follow these steps:

Create a Dockerfile in your project directory with the following content:


dockerfileCopyFROM python:3.9
WORKDIR /app
COPY requirements.txt .

RUN pip install -r requirements.txt

COPY . .
CMD ["python", "app.py"]

Create a requirements.txt file listing your Flask app's dependencies:

Copyflask
# other dependencies

Make sure your Flask app is named app.py & has the following code to run the server:

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

Build the Docker image:

docker build -t my-flask-app .

Run the Docker container:

docker run -p 5000:5000 my-flask-app

Your Flask app will now be accessible at http://localhost:5000.

22. How do you implement WebSockets in a Flask application?

To implement WebSockets in a Flask application, you can use the Flask-SocketIO extension. Here's a basic example:

from flask import Flask
from flask_socketio import SocketIO, emit
app = Flask(__name__)
socketio = SocketIO(app)
@socketio.on('connect')
def handle_connect():
    emit('response', {'data': 'Connected'})
@socketio.on('message')
def handle_message(message):
    emit('response', {'data': message})
if __name__ == '__main__':
    socketio.run(app)

In this example:

We import the necessary classes from flask_socketio
Create an instance of the SocketIO class, passing the Flask app
Define event handlers using the @socketio.on decorator for the 'connect' & 'message' events
Inside the event handlers, use the emit function to send responses back to the client
Run the application using socketio.run(app)

On the client-side, you can use the SocketIO JavaScript library to establish a connection & communicate with the server:

<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.3.2/socket.io.js"></script>
<script>
  const socket = io();
   socket.on('response', function(data) {
    console.log(data);
  });
    socket.emit('message', 'Hello, server!');
</script>

Flask-SocketIO simplifies the implementation of WebSocket communication between the client & server in Flask applications.

23. How do you perform database migrations in Flask with Alembic?

To perform database migrations in Flask using Alembic, you can follow these steps:

Install Flask-Migrate, which integrates Alembic with Flask:

pip install Flask-Migrate

Set up Flask-Migrate in your Flask application:


from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'your-database-uri'
db = SQLAlchemy(app)
migrate = Migrate(app, db)

Initialize the migration repository:

flask db init

This command creates a new "migrations" directory with the necessary files.

Create a migration script:

flask db migrate -m "Initial migration"

This command generates a migration script based on the changes detected in your database models.

Apply the migration to the database:

flask db upgrade
This command applies the migration script to update the database schema.
To revert a migration, use:
flask db downgrade
This command rolls back the database to the previous migration.

With Flask-Migrate & Alembic, you can easily manage database schema changes over time in your Flask application.

24. How do you implement internationalization (i18n) in Flask?

To implement internationalization (i18n) in Flask, you can use the Flask-Babel extension. Here's a step-by-step guide:

Install Flask-Babel:

pip install Flask-Babel

Set up Flask-Babel in your Flask application:

from flask import Flask
from flask_babel import Babel
app = Flask(__name__)
babel = Babel(app)
@babel.localeselector
def get_locale():
    return 'en' # or any other logic to determine the locale

Mark translatable strings in your Python code using the gettext function:

from flask_babel import gettext
@app.route('/')
def index():
    message = gettext('Welcome to my app!')
    return message

Create translation files for each supported language:

pybabel extract -F babel.cfg -o messages.pot .
pybabel init -i messages.pot -d translations -l en
pybabel init -i messages.pot -d translations -l es

These commands extract translatable strings, create a template file (messages.pot) & initialize translation files for English (en) & Spanish (es).

Translate the messages in the generated translation files (e.g., translations/es/LC_MESSAGES/messages.po).

Compile the translations:

pybabel compile -d translations

In your templates, use the _() function to mark translatable strings:

<h1>{{ _('Welcome to my app!') }}</h1>

Set the desired locale in your routes or use the @babel.localeselector decorator to determine the locale based on the user's preferences.

With these steps, Flask-Babel helps you localize your Flask application by managing translations & switching between different languages.

25. How do you implement OAuth authentication in Flask?

To implement OAuth authentication in Flask, you can use the Flask-Dance extension. Flask-Dance provides an easy way to integrate various OAuth providers into your Flask application. Here's an example of using Flask-Dance with GitHub OAuth:

Install Flask-Dance:

pip install Flask-Dance

Set up Flask-Dance in your Flask application:

from flask import Flask
from flask_dance.contrib.github import make_github_blueprint, github
app = Flask(__name__)
app.secret_key = 'your-secret-key'
github_blueprint = make_github_blueprint(
    client_id='your-github-client-id',
    client_secret='your-github-client-secret',
)
app.register_blueprint(github_blueprint, url_prefix='/login')
@app.route('/')
def index():
    if not github.authorized:
        return redirect(url_for('github.login'))
    resp = github.get('/user')
    assert resp.ok
    return 'You are @{login} on GitHub'.format(login=resp.json()['login'])

In this example:

We import the necessary classes from flask_dance.contrib.github
Create a GitHub OAuth blueprint using make_github_blueprint & provide the client ID & secret obtained from the GitHub OAuth application settings
Register the blueprint with the Flask app using app.register_blueprint
In the index route, check if the user is authorized using github.authorized
If not authorized, redirect the user to the GitHub login page using github.login
If authorized, make a request to the GitHub API using github.get to retrieve the user's information
Return a personalized message with the user's GitHub username

Run your Flask application & navigate to the index route. You will be redirected to the GitHub login page for authorization. After successful authorization, you will be redirected back to your application, & the user's GitHub information will be accessible.

Flask-Dance simplifies the OAuth authentication process by abstracting away the complexities of the OAuth flow & providing a straightforward API for interacting with various OAuth providers.

26. Explain the role of request & session objects in Flask.

In Flask, the request & session objects play important roles in handling client-server communication & managing user-specific data.

The request object represents the current HTTP request sent by the client to the server. It contains information about the request, such as:

HTTP method (GET, POST, etc.)
URL parameters
Form data
Headers
Cookies

You can access the request object in your Flask routes to retrieve data submitted by the client. For example:

from flask import request
@app.route('/submit', methods=['POST'])
def submit():
    name = request.form.get('name')
    email = request.form.get('email')
    # Process the submitted data

The session object, on the other hand, represents a secure way to store data specific to each user across multiple requests. It allows you to store & retrieve data on a per-user basis. The session data is stored on the server & is signed using a secret key to prevent tampering.

Here's an example of using the session object:

from flask import session
@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username')
    password = request.form.get('password')
    # Perform authentication
    if authenticated:
        session['username'] = username
        return redirect(url_for('dashboard'))
   @app.route('/dashboard')
def dashboard():
    username = session.get('username')
    if username:
        return f'Welcome, {username}!'
    else:
        return redirect(url_for('login'))

In this example:

Upon successful login, the user's username is stored in the session using session['username'] = username
In the dashboard route, the username is retrieved from the session using session.get('username')
If the username exists in the session, a personalized welcome message is displayed; otherwise, the user is redirected to the login page
The session object provides a way to persist data across requests & maintain user-specific information securely.

Both the request & session objects are essential for building interactive & personalized Flask applications, allowing you to handle user input & manage user state effectively.

27. What is the purpose of Flask-SQLAlchemy?

Flask-SQLAlchemy is an extension for Flask that adds support for SQLAlchemy, a popular SQL toolkit & Object-Relational Mapping (ORM) library for Python. The main purpose of Flask-SQLAlchemy is to simplify database operations & management in Flask applications.

Here are some key features & benefits of using Flask-SQLAlchemy:

Database Abstraction: Flask-SQLAlchemy provides a high-level & Pythonic way to interact with databases. It abstracts away the low-level details of writing SQL queries & allows you to work with databases using Python objects & classes.
ORM (Object-Relational Mapping): With Flask-SQLAlchemy, you can define your database models as Python classes. The ORM maps these classes to database tables & provides an intuitive way to query & manipulate data using object-oriented programming concepts.
Database Connection Management: Flask-SQLAlchemy handles the connection & management of the database for you. It takes care of opening & closing database connections, pooling connections for better performance & providing a simple API for executing database operations.
Database Migrations: Flask-SQLAlchemy integrates with Flask-Migrate, an extension that handles database migrations. Migrations allow you to version control your database schema & easily apply changes to the schema over time as your application evolves.
Multiple Database Support: Flask-SQLAlchemy supports various database backends, including PostgreSQL, MySQL, SQLite & more. You can easily switch between different databases by modifying the database URI in your Flask configuration.
Query Building: Flask-SQLAlchemy provides a powerful query builder that allows you to construct complex queries using a chainable & expressive syntax. You can filter, sort, join & aggregate data easily without writing raw SQL queries.

Here's a simple example of using Flask-SQLAlchemy to define a database model & perform a query:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
db = SQLAlchemy(app)
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
@app.route('/users')
def get_users():
    users = User.query.all()
    return str(users)

In this example:

We import the necessary classes from flask_sqlalchemy
Create an instance of the SQLAlchemy class, passing the Flask app
Define a User model with id, username & email columns
In the /users route, we query all users using User.query.all() & return them as a string

Flask-SQLAlchemy simplifies database management in Flask applications by providing an intuitive ORM, query building capabilities & seamless integration with other Flask extensions.

28. How do you handle large file uploads in Flask?

To handle large file uploads in Flask, you can use the built-in request object along with the Flask configuration options. Here's an example of how to handle file uploads in Flask:

from flask import Flask, request
app = Flask(__name__)
app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024  # 16MB
@app.route('/upload', methods=['POST'])
def upload_file():
    if 'file' not in request.files:
        return 'No file uploaded', 400
    file = request.files['file']
    if file.filename == '':
        return 'No selected file', 400
    if file:
        # Save the file to a desired location
        file.save('path/to/save/file')
        return 'File uploaded successfully'


    return 'File upload failed', 500

In this example:

We set the MAX_CONTENT_LENGTH configuration option to limit the maximum size of the uploaded file. In this case, it's set to 16MB (16 * 1024 * 1024 bytes).
In the upload_file route, we check if a file is present in the request using request.files.
If no file is uploaded, we return an error message with a 400 status code.
We access the uploaded file using request.files['file'], where 'file' is the name of the file input field in the HTML form.
We check if the file has a filename. If it's empty, we return an error message.
If a file is present, we can save it to a desired location using file.save().
Finally, we return a success message if the file is uploaded successfully, or an error message with a 500 status code if the upload fails.

To handle even larger files or to improve upload performance, you can consider the following:

Streaming Uploads: Instead of reading the entire file into memory, you can use request.stream to read the file in chunks. This allows you to handle large files without consuming a lot of memory.
Asynchronous Processing: If the file upload requires time-consuming processing, you can offload the processing to a background task using a task queue like Celery. This ensures that the upload request doesn't block & responds quickly to the client.
Third-Party Libraries: There are Flask extensions like Flask-Uploads that provide additional features & abstractions for handling file uploads, such as file validation, secure filename generation & storage management.

Remember to always validate & sanitize the uploaded files to ensure security & protect against potential vulnerabilities like file path traversal or malicious file uploads.

29. How do you ensure thread safety in a Flask application?

Flask applications are typically deployed using a WSGI server that can handle multiple requests concurrently. However, Flask itself is not thread-safe by default due to the use of global objects like request, session & g. To ensure thread safety in a Flask application, you need to consider the following:

Use Thread-Local Storage: Flask uses thread-local storage to store request-specific data, such as request, session & g objects. This means that each thread has its own copy of these objects, preventing concurrent access issues. Flask automatically manages thread-local storage for you.
Avoid Modifying Shared Data: If your Flask application uses shared data structures or variables that are accessed by multiple threads, you need to ensure proper synchronization & thread safety. Use thread synchronization primitives like locks, semaphores or queues to protect shared data from concurrent access.
Use Thread-Safe Extensions: When using Flask extensions, make sure they are thread-safe. Many Flask extensions, such as Flask-SQLAlchemy & Flask-Login, are designed to be thread-safe out of the box. However, it's important to review the documentation & guidelines of each extension to ensure thread safety.
Implement Application-Level Locking: If your Flask application requires exclusive access to certain resources or performs critical sections of code, you can implement application-level locking. Use thread synchronization primitives like locks or semaphores to enforce exclusive access & prevent race conditions.
Use Asynchronous Processing: For long-running tasks or blocking operations, consider using asynchronous processing techniques like background tasks or event-driven architectures. This allows you to offload time-consuming tasks to separate threads or processes, keeping the main application thread responsive.
Test & Monitor for Concurrency Issues: Thoroughly test your Flask application under concurrent load to identify & fix any potential thread safety issues. Use tools like load testing frameworks or profilers to simulate concurrent requests & monitor for any anomalies or deadlocks.

Conclusion

In this article, we discussed the most-asked Flask interview questions. Hope, from these Flask interview questions, you got a clear idea of the range of questions asked in interviews.

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Introduction

Beginner-Level Flask Interview Questions and Answers

1. What is the difference between Flask & Django?

2. Why do we use Flask(__name__) in Flask?

3. What is routing in Flask?

4. Describe Flask error handlers.

5. Explain the use of context processors in Flask.

6. Why is Flask called a microframework?

7. What HTTP methods does Python Flask provide?

8. How can you make a Flask app asynchronous?

9. In Flask, what do you mean by template engines?

10. What is Flask-Migrate?

Intermediate Level Flask Interview Questions and Answers

11. What is Flask-WTF & what are its characteristics?

12. What is Flask-Migrate & how do you use it?

13. What is the g object in Flask? What distinguishes it from the session object?

14. Mention how you can enable debugging in Flask.

15. How to create a RESTful application in Flask?

16. What is Flask-Sijax?

17. How to get a visitor's IP address in Flask?

18. Explain application context & request context in Flask.

19. How do you handle API versioning in Flask?

20. Explain how you can access sessions in Flask.

Advanced Level Flask Interview Questions and Answers

21. Explain how to deploy a Flask application using Docker.

22. How do you implement WebSockets in a Flask application?

23. How do you perform database migrations in Flask with Alembic?

24. How do you implement internationalization (i18n) in Flask?

25. How do you implement OAuth authentication in Flask?

26. Explain the role of request & session objects in Flask.

27. What is the purpose of Flask-SQLAlchemy?

28. How do you handle large file uploads in Flask?

29. How do you ensure thread safety in a Flask application?

Conclusion

2. Why do we use Flask(name) in Flask?