Top Python Flask Interview Questions and Answers (2025)

by | Oct 8, 2025 | blog | 0 comments

Flask is a lightweight and flexible Python web framework widely used for building web applications and RESTful APIs. Its simplicity, modularity, and ease of integration with other libraries make it a popular choice for developers. If you’re preparing for a Python Flask interview, understanding both fundamental concepts and practical applications is key.

This guide provides a comprehensive list of Python Flask interview questions and answers to help you succeed, whether you’re a beginner or an experienced developer.

Basic Questions

    • What is Flask?
      Flask is a micro web framework written in Python, which allows you to build web applications quickly and with minimal setup.

    • What is a Flask route?
      A route maps a URL to a Python function. For example:

@app.route('/')

def home():

return “Hello, Flask!”

 

    • How do you run a Flask application?

if __name__ == '__main__':

app.run(debug=True)

 

    • What is the difference between Flask and Django?
      Flask is lightweight and flexible with fewer built-in features, while Django is a full-featured framework with ORM, authentication, and admin panel.

    • What are Flask templates?
      Flask uses Jinja2 templates to dynamically generate HTML pages.

    • What is the role of Flask object?
      It acts as the core application object and is used to configure routes, error handlers, and extensions.

    • How do you pass data from Flask to templates?
      Using the render_template function:

from flask import render_template

@app.route(‘/’)

def home():

return render_template(‘index.html’, name=“John”)

 

    • What is Flask-SQLAlchemy?
      It’s an extension that simplifies database operations using SQLAlchemy ORM.

    • How do you handle form data in Flask?
      Using request.form for POST requests:

from flask import request

@app.route(‘/submit’, methods=[‘POST’])

def submit():

name = request.form[‘name’]

 

    • What is a Flask Blueprint?
      Blueprints allow you to organize Flask applications into modular components.

Intermediate Questions

    • Explain Flask request lifecycle.
      It starts with the HTTP request, routing, middleware processing, view function execution, template rendering, and finally sending a response.

    • How do you manage sessions in Flask?
      Flask uses signed cookies to store session data via the session object:

from flask import session

session[‘username’] = ‘john’

 

    • What are Flask decorators?
      Decorators are used to modify the behavior of a function or route, e.g., @app.route('/').

    • Explain URL converters in Flask.
      They define the type of variable in a route:

@app.route('/user/<int:id>')

def user(id):

return f”User {id}”

 

    • How do you handle errors in Flask?
      Using error handlers:

@app.errorhandler(404)

def page_not_found(e):

return “Page Not Found”, 404

 

    • What is Flask-WTF?
      It’s an extension for handling forms, validation, and CSRF protection.

    • How can you serve static files in Flask?
      Place them in the static folder and access via /static/<filename>.

    • Explain Flask configuration methods.
      Configurations can be set using app.config['KEY'], environment variables, or separate config files.

    • How do you redirect in Flask?

from flask import redirect, url_for

return redirect(url_for(‘home’))

 

    • What is Flask-Migrate?
      An extension for handling database migrations using Alembic.

Advanced Questions

  1. Explain middleware in Flask.
    Middleware is a function that runs before or after a request to process it, often used for logging or authentication.
  2. How do you implement authentication in Flask?
    Using Flask-Login or JWT tokens for session management and protected routes.
  3. Explain context in Flask (Application and Request context).

    • Application context holds current_app and g objects.

    • Request context holds request and session objects.

  1. How to handle file uploads in Flask?
    Using request.files and saving files securely:

file = request.files['file']

file.save(‘/uploads/’ + file.filename)

 

  1. Explain how to create RESTful APIs in Flask.
    Use Flask routes with HTTP methods (GET, POST, PUT, DELETE), optionally with Flask-RESTful extension.
  2. What is Flask’s g object?
    A global namespace for storing data during a request lifecycle.
  3. Explain signal handling in Flask.
    Flask signals (via Blinker) allow decoupled components to respond to events like template rendering.
  4. How to implement caching in Flask?
    Using Flask-Caching or third-party caching solutions like Redis.
  5. How can you secure a Flask application?
    Use HTTPS, secure cookies, CSRF protection, input validation, and proper error handling.
  6. Explain async support in Flask 2.x.
    Flask now supports asynchronous view functions using async def, improving performance for I/O-bound tasks.

Scenario-Based Questions

  1. You need to create a multi-page website with reusable components. How would you structure it?
    Use Blueprints to modularize the app, templates with inheritance, and static folders for assets.
  2. Handling high traffic API with Flask

    • Use Gunicorn or uWSGI as WSGI servers

    • Enable caching for frequent responses

    • Use a database connection pool

  1. Migrating a Flask app to production

    • Use environment-specific config

    • Enable logging

    • Configure HTTPS and reverse proxy with Nginx or Apache

Conclusion

Preparing for Python Flask interviews requires a mix of theory and hands-on practice. Focus on routing, templates, database interactions, and real-world application design. Practicing scenario-based questions will give you confidence for practical problems.

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