Flask Interview Questions

Flask is a lightweight WSGI web application framework in Python, known for its simplicity and flexibility.

It is a micro-framework with no built-in ORM, form validation, or admin interface, giving developers freedom to choose tools and structure.

Django is a full-featured framework with batteries included, including ORM, admin panel, and form handling.

Flask is ideal for small applications, APIs, and microservices, while Django suits large, feature-rich applications with database-driven content.

Jinja2 is the templating engine used by Flask for rendering dynamic HTML pages.

It allows embedding Python-like expressions and control structures within HTML templates.

Features include template inheritance, macros, filters, and auto-escaping to prevent XSS vulnerabilities.

Templates are rendered using the render_template() function with context variables passed from routes.

Blueprints in Flask are a way to organize large applications into reusable components.

They allow grouping of routes, templates, and static files into logical units, similar to apps in Django.

Blueprints help maintain clean code structure, modular design, and scalability.

They are registered with the Flask app using app.register_blueprint() and support URL prefixes and subdomains.

Flask does not include a built-in ORM, but SQLAlchemy and Peewee are popular choices for database interaction.

Flask-SQLAlchemy and Flask-Migrate extensions simplify ORM usage and database migrations.

Database setup usually involves initializing a connection, defining models, and performing CRUD operations via session objects.

Flask supports SQLite, PostgreSQL, MySQL, and other databases through adapter libraries.

Flask-WTF is an extension that integrates WTForms with Flask for handling HTML forms.

It provides form validation, CSRF protection, and field rendering helpers.

Forms are defined as Python classes and validated before processing.

Flask-WTF simplifies form handling, making it secure and easy to manage.

Flask-RESTful is an extension that simplifies building REST APIs with Flask.

It provides Resource class-based views, request parsing, and error handling out of the box.

APIs are defined with routes and HTTP methods mapped to resource methods (get, post, put, delete).

Flask-RESTful is ideal for building scalable, testable, and maintainable RESTful services.

The application context in Flask is used to access the current application and its configuration during a request or background task.

It is created using app.app_context().push() and destroyed with pop().

It holds application-wide data like configuration, database connections, and extensions.

It is essential for working with Flask outside of request contexts, such as in command-line scripts or background jobs.

Flask-Caching is an extension that adds caching support to Flask applications.

It supports various backends like Redis, Memcached, and filesystem-based caching.

Caching is used to improve performance by storing frequently accessed data in memory or external stores.

It can be applied at view level, function level, or custom-defined intervals.

Flask-Caching is ideal for speeding up repeated queries, API responses, and page renders.

In Flask, the request context is active during a request and provides access to request-specific data like request, session, g, and current_app.

The application context is active during app startup or background tasks and provides access to app-level data like config, extensions, and database connections.

These contexts allow Flask to manage global variables in a thread-safe manner.

They are automatically pushed and popped during requests, but must be managed manually in CLI scripts or background workers.

Flask applications can be deployed using Gunicorn, uWSGI, Waitress, or other WSGI servers behind Nginx or Apache.

Deployment options include bare metal, VMs, containers (Docker), PaaS (Heroku), and serverless (Lambda + API Gateway).

Tools like Fabric, Ansible, and Docker Compose automate deployment processes.

For production, use a reverse proxy, SSL termination, and process managers like systemd or supervisor.