In 2026, Flask continues to stay relevant as one of the most trusted and popular Python micro-frameworks, especially for lightweight web apps, REST APIs, and even for AI-driven backend services.
Despite the launch of many new frameworks, companies are still relying on Flask for its simplicity, flexibility, and strong ecosystem. This is why Flask questions remain a common part of Python interviews.
In this guide, you will find the top 50 Flask Interview Questions that can be asked in 2026, selected from Reddit forums, Facebook dev communities, and other social media platforms where candidates posted their true experiences.
As Python experts, we ensure that multiple questions from this list are highly likely to be asked in your next interview. Prepare these well, and best wishes in advance.
Flask Interview Questions Full Index
Flask Foundations, Architecture, and Key Features
This section covers the core definitions, fundamental components, setup, and key architectural differences that define Flask.
1. What is Flask, and why is it called a microframework?
Flask is a lightweight Python web framework designed to make web development simple and flexible. It provides a programming interface for building web applications and is based on the WSGI toolkit and the Jinja2 template engine.
Flask is called a “microframework” because of its core design philosophy, not its capability to handle large applications. The term means that Flask focuses only on the minimum necessary core web application functionality, such as routing and request processing. It intentionally leaves advanced features like authentication, form validation, or database management to extensions. This design allows us the flexibility to choose and integrate only the components we need for a specific project, which makes Flask highly scalable and versatile for diverse project types.
2. How does Flask differ from a full-stack framework like Django?
The difference lies primarily in their architectural philosophies and the tools they provide out of the box. Flask is a microframework, meaning it is minimalistic and non-opinionated, providing us only the basic tools for web development. We must add other features through extensions, like using Flask-SQLAlchemy for database operations.
Django, in contrast, is a full-stack framework that follows a “batteries-included” philosophy. It comes with many built-in components, such as a powerful Object-Relational Mapper (ORM), an admin interface, and integrated authentication systems. Django’s conventional project structure is suitable for larger projects that need a standardized setup. Flask gives us more control and is ideal for specialized RESTful APIs and microservices, while Django is often preferred for large, feature-rich web applications.
3. What is WSGI, and how is it related to Flask?
WSGI stands for Web Server Gateway Interface. It is a critical specification in Python that defines a standardized way for web servers (like Nginx or Apache) to communicate with Python web applications (like Flask).
Flask is specifically designed to be a WSGI-compliant framework. This compliance is fundamental because it allows us to deploy our Flask application using any standard WSGI-compatible web server, such as Gunicorn or uWSGI. WSGI compliance ensures that Flask applications can handle requests and responses in a standardized, performant way when deployed in a real-world production environment.
4. Why do we pass __name__ when initializing a Flask application?
We initialize a Flask application using the built-in Python variable __name__ as the primary argument, like this: app = Flask(__name__).
Passing __name__ helps Flask correctly determine the root path of the application. This is essential because Flask needs to know where to look for associated resources, specifically the templates folder for HTML files and the static folder for CSS, JavaScript, and image assets. By using __name__, Flask automatically figures out the location of these supporting files relative to the main module, which is crucial for organization, especially when we use Blueprints to divide the application into multiple files.
5. What are some of the key features of the Flask framework?
Flask is popular due to its simplicity and powerful core features. Key features include compliance with the Web Server Gateway Interface (WSGI), which ensures deployment compatibility.
Other important features are a built-in web server and a visual debugger that significantly speeds up troubleshooting during development. Flask provides robust URL routing through view functions, integrates the powerful Jinja2 templating engine for dynamic content, and offers excellent support for building RESTful APIs. It also provides integrated support for unit testing and flexibility to extend its functionality easily using many community-maintained extensions.
6. What is the default local host and port number for a Flask development server?
When we run a Flask application using app.run() without specifying any parameters, the default local host is 127.0.0.1. The default port number used is 5000.
The address 127.0.0.1 is the standard loopback address, meaning the application server is accessible only from the local machine we are working on. Port 5000 is the standard choice for development environments, but we can easily change this when running the application, which is helpful if we need to run several local applications at the same time.
7. Explain the role of the app.run() method in Flask.
The app.run() method is a utility used during development to start the Flask development server.
When we execute this method, the server begins listening for incoming HTTP requests and routes them to the appropriate Python view functions within our application. It is essential to remember that this built-in server is designed purely for testing and debugging. The critical distinction is that this simple server is not robust enough for the performance, stability, or security requirements of production environments. When deploying the application live, we must use a professional WSGI server like Gunicorn.
8. How do you create a basic “Hello, World!” application in Flask?
Creating the simplest application in Flask requires four basic steps: importing the Flask class, creating an application instance, defining a route, and running the application.
We first import the Flask class, then create an instance of the application, passing __name__. We define the root URL (/) using the @app.route('/') decorator, which ties the URL to a Python function. This function, known as a view function, returns the response, such as the text “Hello, World!”. Finally, the app.run() method starts the development server, allowing us to access the simple application in a web browser. This minimal code structure reinforces the “microframework” concept by showing how few lines are needed to get a web application working.
9. What is the purpose of the built-in development server and debugger in Flask?
Flask includes both a development server and a powerful visual debugger.
The development server is crucial because it allows us to quickly start and test our application locally, providing a sandbox for rapid testing and iteration. The visual debugger is immensely useful during the coding phase because it provides interactive access to the application stack and variables when an unhandled exception or error occurs. This interactive debugging feature helps developers pinpoint and fix bugs much faster than relying only on static error messages, which significantly speeds up the process of development.
10. What types of applications are best suited for development using Flask?
Flask is versatile and can be rapidly combined with other technologies to build almost any kind of web application, but it excels in several specific areas.
Flask is ideal for building RESTful API-based applications and high-performance microservices, due to its minimalistic design and strong support for dispatching RESTful requests. It is also highly suited for developing small to medium web applications, static websites, and rapidly building prototypes (Minimum Viable Products). Its flexibility makes it a great choice for specialized systems like Machine Learning inference servers or serverless applications.
Routing, Request Handling, and HTTP Methods
This section covers how Flask processes incoming traffic, defines URL pathways, and handles different data submission methods essential for creating interactive web services.
11. What is routing in Flask, and how is it implemented?
App routing is the fundamental process of mapping incoming URLs (Uniform Resource Locators) to specific Python functions, known as view functions, that will execute the necessary logic for that URL.
Modern web frameworks, including Flask, use meaningful URLs to help users remember the paths and make navigation simpler. This is implemented using the Python decorator pattern. The @app.route() decorator is used to associate a specific URL pattern directly with the view function that should be executed when a client requests that path. Flask’s routing system is one of its most appreciated features because it is flexible and easy to use.
12. What is the purpose of the @app.route() decorator?
The @app.route() decorator is the primary mechanism for defining the endpoints and the structure of our Flask application.
Its purpose is to register a URL endpoint with the Flask application, effectively binding a specific URL pattern to a Python function. When a request hits the Flask application, the decorator tells the framework exactly which view function should be executed to handle that request and return a response. For instance, @app.route('/login') maps the /login path to the login function.
13. How do you define a route that accepts dynamic parameters in the URL?
Flask allows us to include dynamic, or variable, parts directly within the URL path definition. We achieve this by enclosing the variable name within angle brackets (< >) in the route URL.
For example, a route defined as @app.route('/user/ will accept any text input for the username part of the URL. Flask automatically extracts this value (for example, “alice”) and passes it as a keyword argument to the corresponding view function. This mechanism makes it simple to create resource-specific pages, like profile pages or item details, without having to define a separate, static route for every possible user or item.
14. Explain what the url_for() method does in Flask and why it is useful.
The url_for() method is a utility function used to dynamically create a URL that points to a specific view function.
The first argument provided to url_for() is the name of the desired function. If the route for that function contains dynamic parts, we pass those values as keyword arguments. The function is useful because it prevents us from writing URLs directly, or hard-coding them, into our templates or code. If we later change a URL path defined by a decorator, all calls to url_for() throughout the application automatically update the generated link. This flexibility drastically reduces maintenance effort and prevents broken links in our application.
15. Describe the use case for the HTTP GET method in Flask.
GET is the most commonly used approach among all HTTP methods. It is strictly used to retrieve or request data from the server.
Examples of GET requests include accessing a homepage, viewing a list of blog posts, or fetching the details of a single product. Because GET requests should never modify the server’s state or data, they are considered “safe” operations. This property also means that responses from GET requests can often be cached by browsers or proxy servers, which improves application performance and reduces server load.
16. Describe the use case for the HTTP POST method in Flask.
The POST method is used when we want to submit data to the server, typically when handling data received from an HTML form.
POST requests are used for actions that create or update a resource on the server, such as submitting a login form, signing up a new user, or uploading a new file. Unlike the GET method, which passes data via the URL, POST requests carry the payload data within the request body, which is generally considered a more secure way to transmit information.
17. What are the purposes of the HTTP PUT and DELETE methods in RESTful Flask applications?
The PUT and DELETE methods are crucial for building applications that follow the principles of REST (Representational State Transfer).
The PUT method is used to upload content that completely replaces all current representations of the target resource identified by the URL. If the resource exists, it is updated, if it does not, it may be created. The DELETE method is reserved exclusively for removing all current representations of the URL’s target resource. These methods are foundational for building clean, organized APIs where resources are managed through clear, standard HTTP verbs.
18. What is the request object in Flask, and how do we access form data?
The request object in Flask is an instance of the Request class that encapsulates all the information about an incoming HTTP request. This information includes details like headers, cookies, file uploads, and submitted form data.
The request object is available globally within the Request Context. We access form data submitted via a POST request using the request.form attribute. This attribute behaves like a dictionary, allowing us to easily retrieve specific field values by their name, for example, request.form['username'].
19. How can you get an argument’s value from the URL query string in Flask?
Query string parameters are the pairs of keys and values that appear in the URL after a question mark (?), often used for filtering, searching, or sorting data.
In Flask, we access these parameters using the request.args attribute. This attribute also acts like a dictionary. It is considered a safer programming practice to use the .get() method when retrieving query string values, such as request.args.get('search_term'), because if the parameter is missing from the URL, the application will not crash, but rather return a default value like None.
20. How do you retrieve the visitor’s IP address within a Flask view function?
To obtain the IP address of the client that is making the request to our Flask application, we use the request.remote_addr method.
This attribute provides the network address of the visitor. This information is a fundamental part of managing web traffic and is needed for practical tasks like logging user access, implementing security measures such as rate limiting to prevent abuse, or performing basic geographic filtering based on location.
Contexts, Sessions, and State Management in Flask
This crucial section addresses Flask’s unique approach to state isolation and concurrency, covering contexts and the special thread-local objects. These concepts are often included in advanced Flask interview questions.
21. Explain the concept of the Application Context in Flask.
The Application Context is the environment in which the entire Flask application runs. It is created when the application starts and destroyed when it shuts down.
The main purpose of the Application Context is to make application-level resources, such as the configuration settings and logging setup, available globally via the current_app proxy. This prevents us from having to pass the application instance directly into every single function that needs access to the configuration. The Application Context is useful even when no HTTP request is being processed, such as when running custom command-line interface (CLI) commands or initialization scripts.
22. Explain the concept of the Request Context in Flask.
The Request Context is the environment specifically created for processing a single, individual request. It is automatically created when an HTTP request arrives and is destroyed immediately after the response is sent back to the client.
The Request Context is responsible for wrapping the incoming request and ensuring that all data related to that specific client interaction, such as the URL, the HTTP method, headers, and form data, is easily accessible to the view function. This information is accessed via the request proxy object. The Request Context is crucial because it ensures that simultaneous users running concurrent requests do not accidentally access or interfere with each other’s data, maintaining data isolation.
23. What is the g object in Flask, and what is its primary use?
The g object is a simple namespace object provided by Flask that is used for temporary storage. The name g stands for “global,” referring to the data being global within the current context.
The primary purpose of the g object is to share data efficiently between different functions and parts of the code during the lifespan of a single request. A common and important use case for the g object is storing resources that are expensive to create, such as a database connection. We can initialize a database connection once at the beginning of the request and cache it on g. All subsequent functions requiring database access can retrieve the connection from g, thus avoiding repeated creation and destruction of connections, which improves overall performance.
24. What is the difference between the session object and the g object in Flask?
The difference between the session object and the g object lies fundamentally in their scope and persistence.
The g object’s data is temporary and exists only for the duration of a single request or application context. Once the response is sent, the data on g is lost forever. The session object, in contrast, is designed to persist data across multiple requests from the same user or client. It stores information like the user’s login status, preferences, or shopping cart contents, often storing this data securely in a cookie on the client side.
25. How do you enable and access session data in a Flask application?
To enable session functionality, we must first configure a strong and unique SECRET_KEY in our application configuration. This key is essential for security because it cryptographically signs the session data that is stored in the cookie, preventing users from tampering with the session contents.
Once configured, session data is easily accessed and modified using the session object within any view function. The session object behaves exactly like a standard Python dictionary, allowing us to store and retrieve data simply by assigning keys and values, for example, session['username'] = 'John'.
26. Explain how Flask handles cookies, and how you can set a cookie.
Cookies are small text files that are stored on the client’s PC (the user’s browser) and are primarily used to track user actions or store preferences.
In Flask, cookies are set by modifying the response object before it is sent back to the client. To set a cookie, we first create a response object using the make_response() method from the view function. We then use the response.set_cookie('key', 'value') method on that response object, specifying the cookie name and its value.2 This mechanism allows Flask to manage client-side state effectively.
27. What happens to the Application Context and Request Context when a request finishes?
When an HTTP request is completed and the final response is generated and sent to the client, Flask performs a systematic cleanup process. Both the Request Context and the Application Context are “popped,” or destroyed, in sequence.
Immediately before they are popped, Flask executes any registered teardown_request() and teardown_appcontext() functions. This teardown process is critical because it ensures that all temporary resources, such as database connections that were stored on the g object, are properly closed or released. Proper context cleanup prevents resource leaks and guarantees the necessary thread safety for concurrent operations.
28. What are thread-local objects in Flask, and why are they used?
Thread-local objects in Flask, such as request and g, are mechanisms implemented using Python’s contextvars and Werkzeug’s LocalProxy.
They are used to provide data isolation in a concurrent environment. Flask allows us to write code as if we were accessing global variables (for example, simply using request.form), which maintains code simplicity. However, the thread-local mechanism guarantees that the data accessed is strictly isolated to the specific thread or worker process handling the current request. This engineering backbone ensures that if multiple users access the application simultaneously, they do not accidentally access or corrupt each other’s temporary data, making Flask safe for concurrency.
29. What is a common scenario where you would use the Application Context manually?
Normally, Flask automatically pushes the Application Context when it starts handling an HTTP request or runs a CLI command.
However, there are scenarios where we need to manually activate the context. This is typically required when running maintenance tasks, debugging sessions, batch scripts, or customized command-line interfaces that exist outside of a standard HTTP request cycle. Manual context activation is necessary to allow the script to access application configuration, logging settings, or initialize extensions like the database manager, all of which depend on the current_app proxy being available.
30. How do you configure a secret key in Flask, and why is it essential for security?
The secret key is configured by setting the SECRET_KEY variable within the application’s configuration, usually in app.config.
The secret key is essential for security because it serves as the cryptographic key used to sign all client-side session data and cookies. This signing process creates a secure hash that verifies the integrity and authenticity of the session information stored in the cookie. Without a robust, unique secret key, an attacker could easily forge session cookies or tamper with data, potentially leading to identity theft or unauthorized actions. Therefore, setting the secret key correctly, often using a long, random value stored in an environment variable, is a top priority for any Flask application security review.
Templates, Data Flow, and Forms
These Flask interview questions address how Flask creates dynamic user interfaces and integrates essential components for handling user input and data persistence.
31. What is Jinja2, and how does Flask utilize it for templating?
Jinja2 is a widely used and powerful web template engine for the Python programming language. It is the default templating system utilized by Flask.
Flask utilizes Jinja2 to effectively separate the application logic (the Python code that handles data) from the visual presentation layer (the HTML structure presented to the user). Jinja2 allows us to embed programming structures like loops, conditional statements, and variables directly into HTML files. This capability enables us to dynamically generate the user interface by injecting data processed by the server directly into the structure viewed by the client.
32. Explain what Template Inheritance is and why developers use it.
Template Inheritance is a powerful feature of the Jinja2 templating engine. It is a system designed to manage the common elements that are shared across multiple pages of a website, such as a standardized navigation bar, footer, or basic HTML structure.
Developers use Template Inheritance to promote code reuse and consistency. Instead of repeatedly creating the same HTML head, title tags, and footers on every single webpage, we define a single base layout template. Specific pages then only need to define the unique content blocks they contain, inheriting the rest of the standard structure from the base template. This significantly reduces redundant code and standardizes the look and feel of the entire application.
33. How do you pass data from a Flask view function to an HTML template?
Data is passed from a Flask view function to an HTML template using the render_template() function.
We first specify the name of the template file we wish to render as the first argument in render_template(). We then pass any required data variables as keyword arguments to the function, for example, render_template('page.html', user_list=users). These Python objects, lists, or dictionaries are then injected directly into the Jinja2 context. Inside the template, the developer can access and display this dynamically generated data to the user using Jinja2 syntax.
34. What is Flask-WTF, and how does it simplify form handling?
Flask-WTF is a dedicated Flask extension that provides simple integration with the powerful WTForms package. WTForms is a popular Python library used for creating interactive user interfaces and handling data submission.
Flask-WTF simplifies form handling by allowing us to define forms, their fields, and complex validation rules directly in Python classes, instead of relying solely on raw HTML processing in view functions. This centralizes the validation logic and removes complex data retrieval code from the main application logic, which results in cleaner, more maintainable, and structured code.
35. What security feature does Flask-WTF automatically provide for web forms?
The most critical security feature that Flask-WTF automatically delivers is protection against Cross-Site Request Forgery (CSRF) attacks.
CSRF attacks trick a user’s browser into executing unwanted actions on a web application where the user is currently authenticated. Flask-WTF secures all forms by automatically adding a hidden input field containing a unique and cryptographically secure CSRF token. When the form is submitted, Flask-WTF verifies that this token is correct, ensuring that the submitted data must originate from our actual, legitimate website and not from a malicious external site. This feature is a fundamental security requirement for any production web application.
36. Explain the process for handling file uploads in Flask.
File uploading in Flask is the process of safely sending files from a client browser to the server.
The process begins on the client side, where the HTML form used for the upload must have its encryption type set to multipart/form-data. On the server side, the Flask application uses the request.files object to receive the uploaded file data. We must then retrieve the file object and, importantly, use security functions like secure_filename() to safely handle the filename before saving the file to a designated location on the server. This step prevents dangerous file names or path manipulation attacks.
37. What is the use of jsonify() in Flask, and when should it be used?
The jsonify() function is a helper method found in the flask.json module. Its primary use is to correctly convert Python data structures (like dictionaries or lists) into the globally accepted JSON string format.
jsonify() is essential when we are creating RESTful APIs. It automatically packages the converted JSON data into a response object and critically sets the correct response headers and the MIME type to application/JSON. This standardization guarantees that client applications, such as mobile apps or JavaScript frontends, can correctly interpret the data returned by the server.
38. How can you connect a Flask application to a database like PostgreSQL or MySQL?
Since Flask is a microframework and does not include a built-in database component, we rely on extensions to manage database connections.
The recommended and standard approach for connecting to relational databases (RDBMSs) like PostgreSQL, SQLite, or MySQL is to use an Object-Relational Mapper (ORM) such as SQLAlchemy. We use the Flask-SQLAlchemy extension, which simplifies the integration of SQLAlchemy into the Flask environment. This extension handles the necessary configuration of the database connection URI (address) and manages the database session life cycle, making data operations consistent and simple.
39. What is the primary role of Flask-SQLAlchemy?
The primary role of Flask-SQLAlchemy is to provide an easy-to-use and streamlined interface for working with SQL databases within Flask applications.
It acts as an integration layer, connecting our Flask application directly to the database using an ORM. This abstraction allows developers to define and manipulate data using familiar Python classes and methods rather than requiring them to write complex or time-consuming raw SQL queries. By managing database connections and sessions effectively, Flask-SQLAlchemy enhances application stability and reduces the risk of common database-related errors.
40. What is an Object-Relational Mapper (ORM)?
An Object-Relational Mapper, or ORM, is a programming tool that translates the object-oriented structure of our Python application into the relational structure of a database, such as a SQL database.
The central idea behind an ORM is to allow developers to interact with the database using high-level language objects instead of writing specific SQL commands. For example, instead of writing SQL to fetch users, we can use a Python command like User.query.all(). This translation allows developers to focus on application logic using familiar Python syntax, while the ORM manages the complex details of generating, executing, and retrieving data using SQL in the background.
Modularity, Security, and Production Deployment
This final, advanced section covers architecture for growth, application security, testing protocols, and the essential steps needed to move a Flask application into a live production environment. These topics are crucial for answering senior Flask interview questions confidently.
41. What is a Flask blueprint, and how does it help organize large applications?
A Flask blueprint is a method for organizing a Flask application into smaller, modular, and reusable components.
As a Flask application expands in complexity, keeping all routes, view functions, and logic within a single file or module quickly becomes unmanageable. Blueprints solve this problem by allowing us to modularize the application based on functionality. For example, we can create separate blueprints for user authentication, a blog section, and an administrative panel. Each blueprint can define its own routes, templates, and static files, and it can be registered with the main application. This structure keeps code clean, manageable, and highly maintainable, facilitating teamwork and long-term development.
42. How do you create a RESTful API using Flask?
We can build a RESTful API using raw Flask by defining routes that handle specific HTTP methods (GET, POST, PUT, DELETE) and returning JSON data using jsonify().
However, the professional and recommended approach is to use the Flask-RESTful extension. Flask-RESTful simplifies API creation by providing a structured way to define resources (like /users or /items) using Python classes. In this class-based approach, each method within the class (e.g., get() or post()) automatically corresponds to the required HTTP operation, ensuring adherence to standard REST principles and simplifying data serialization and response handling.
43. What is Flask-RESTful, and what benefits does it offer?
Flask-RESTful is a specialized Flask extension that provides tools and conventions specifically designed for quickly building RESTful APIs.
The main benefit it offers is an abstraction layer that makes defining and serving APIs quicker and more intuitive compared to writing boilerplate code in raw Flask. It standardizes API implementation by managing complexity, such as defining multiple routes for a single resource (e.g., one route for a list of items and another for a single item by ID). It also ensures that API responses are correctly formatted and accompanied by the right HTTP status codes for robust client communication.
44. What are some common security best practices when building Flask applications?
Flask, like any web framework, requires constant attention to security to protect user data and prevent vulnerabilities. Common best practices include:
First, always deploy the application over HTTPS to encrypt all traffic and prevent man-in-the-middle attacks. Second, we must use Flask-WTF to implement automatic CSRF protection, safeguarding against cross-site request forgery attacks. Third, we should rigorously validate and sanitize all user inputs before processing them or inserting them into a database, which prevents various injection attacks. Fourth, the SECRET_KEY used for session signing must be complex, unique, and stored securely in environment variables, never hard-coded within the application source files.
45. How do you handle and customize error pages for common HTTP errors in Flask?
We handle errors in Flask using its built-in error-handling functionality, which allows us to define custom error pages and specific handlers for different types of errors.
Instead of letting an application crash or display a generic error message, we can use the @app.errorhandler(error_code) decorator to define a dedicated view function that activates when a specific HTTP error occurs, such as 404 (Page Not Found) or 500 (Internal Server Error). This ensures a much more professional and controlled user experience, even when things fail. Furthermore, by defining custom handlers, we prevent the application from exposing sensitive technical details to the public during an unexpected failure.
46. Explain the importance of logging in a Flask application.
Logging is essential for monitoring the application’s behavior and health, especially once it is deployed in a production environment. Flask logging gives developers the necessary capabilities to construct sophisticated event-logging systems for their applications.
Since Flask integrates with the standard Python logging framework, it allows different modules to easily communicate and contribute data during the logging process. If a runtime error occurs that was not foreseen or caught during development, logs provide an indispensable, timestamped record of events, variable states, and user actions, which is necessary to diagnose and debug issues remotely.
47. What method is recommended for testing Flask applications?
The recommended method for thoroughly testing Flask applications is through unit testing and integration testing, often utilizing Python libraries such as unittest or pytest.
Flask is designed from the core to support testing easily, providing integrated support for unit testing. We use testing to verify that individual components of the code, such especially view functions, complex logic, and data processing handlers, perform exactly as we expect them to under various scenarios before the application is deployed. This proactive verification significantly reduces the chance of introducing bugs into the live system.
48. Describe the role of the Flask Test Client in unit testing.
The Flask Test Client is an indispensable component provided by the framework for conducting integration testing.
Its role is to simulate incoming HTTP requests to the application without the need to run a live web server or open up network ports. The Test Client provides methods that match common HTTP verbs (such as client.get() or client.post()). This allows our test code to make simulated requests directly to the Flask application instance. By testing the application this way, we can verify that routing, request handling, and response generation all work correctly and efficiently, speeding up the entire testing workflow significantly.
49. What are popular production WSGI servers used to deploy Flask, such as Gunicorn or uWSGI?
Because the built-in Flask development server (app.run()) is neither secure nor performant enough for public traffic, we must use a professional WSGI application server for production.
Popular choices are Gunicorn and uWSGI. Gunicorn (Green Unicorn) is highly favored in the Python community for its simplicity, lightweight design, and robust process management capabilities. uWSGI is another extremely robust and feature-rich server, often selected for very high-performance deployments, typically paired with a dedicated web server like Nginx. Both options are fully WSGI-compliant, which confirms Flask’s readiness for large-scale production use.
50. Describe the general steps involved in deploying a Flask application to a live server.
Deploying a Flask application is typically a multi-layered process involving specialized software. The general steps are:
First, we must install all necessary Python dependencies, typically listed in a requirements.txt file, in the production environment. Second, we choose and configure a WSGI application server, such as Gunicorn, to run the Flask application instance, handling the backend processing. Third, we configure a dedicated web server, such as Nginx or Apache, to act as a reverse proxy. This proxy faces the public internet, handles static files efficiently, and securely forwards incoming client requests to the Gunicorn instance running in the background. Finally, a process manager, like systemd or supervisor, is set up to ensure that the Gunicorn process is running continuously and restarts automatically if it crashes, guaranteeing application stability.
Conclusion
If you have reached the end, you are already ahead of most candidates preparing for Flask interview questions. If you find some Flask interview questions difficult, try to revise the basics, starting with a Hello World app and progressing to a simple CRUD application.
Going through these articles takes only a couple of minutes but gives you enough foundational understanding to confidently answer real interview questions:
