Flask Interview Questions and Answers

Ques 1. What is WSGI?

The full form of WSGI is Web Server Gateway Interface. This is actually a Python standard in PEP 3333. It provides the protocol for web servers to communicate with a web application. 

It mainly plays a role at the time of project deployment.

Ques 2. What is Flask-wtf?

It provides an easy integration process with WTForms.

Ques 3. What features are available in Flask-wtf?

A few features are as follows:

1. Integration with WTForms.
2. CSRF token provides security globally.
3. Provide Recaptcha.
4. File upload facility.

Ques 4. How can we integrate any API like Facebook with the Flask application?

We can integrate it easily with the help of the Flask extension named Flask-Social. It gives multiple access to users for other social platforms also. One thing we need to remember is that we have to use the Flask-Security extension of Flask for security purposes. For this, we need to install all social API libraries in Python. We have to register from an external API service provider.

Ques 5. Can you briefly talk about the Flask template engine?

The Flask template engine allows developers to create HTML templates with placeholders for dynamic data. Actually, a template is a file that contains two types of data, one is static and another is dynamic. Mostly this dynamic template is popular because the data is in run time. Flask allows the Jinja2 template engine to be used mostly as a template engine. Flask’s render_template method needs parameters and their values. 

Ques 6. What are the features of forms extension in Flask?

We have to use the Flask- extension to implement forms in Flask. It’s called WTForms. It’s a Python-based rendering and validation library. It does data validation, CSRF protection, and internationalization. Once we use Flask-uploads, ReCaptcha from Flask-WTF helps to upload files. We can also manage JavaScript requests and customization of error responses.

Ques 7. Explain the G object in Flask?

If we want to hold any data during the application context, the Flask g object is used as a global namespace for keeping any data. It’s not suitable for storing data within requests. Actually, this letter g stands for global. Suppose we need to store a global variable in an application context, then g object is best in place of creating global variables. Here the g object will work as a request in a separate Flask g object. It always saves self-defined global variables.

Ques 8. How can we create request context in the flask?

It can be created in two easy steps. They are:

1. It can be created on its own when the application receives a request from the system.
2. We can do it manually by calling app.test_request_context

Ques 9. Explain Flask Sijax.

It’s an inbuilt library in Python, making it easy for Ajax to work in web applications. Sijax uses JSON while passing data to a server called by the browser.

Ques 10. How can we structure a huge big flask application?

We need to follow the steps below to structure a huge big flask application:

1. We need to move the functions to different files until the applications get started.
2. We need to use the blueprint to view the categories like auth and profile.
3. We need to register all functions on a central URL map using the Werkzeug URL.

Ques 11. What is the utilization of jesonify() in a flask?

This is one of the functions under the flask.json module. It can convert data to JSON and store it in the response object. It provides a response object with an application where json.dumps() only returns a JSON data string.

Ques 12. Describe Flask memory management.

Memory management handles memory allocation in Python. Flask has a built-in garbage collector. It collects all wastage data and makes the space free. It manages memory by private heap space. This is not accessible by developers.

Few of them are accessed by users by using a few API tools. All data allocation is done by Flask memory management.

Ques 13. What do you know about the validators class of WTForms in Flask?

A Validator can take the input to check if it meets some criteria like string limit with returns. In case of failure, a validation error will come. This is a straightforward method. In Flask there are a few validator classes of WTForms. They are:

1. DataRequired: Checks the input field.
2. Email: It checks the email id conventions.
3. IP Address: It checks the IP address.
4. Length: It validates the string length with the given range.
5. NumberRange: It validates the number in the input field with the given range.
6. URL: Checks the URL input field.

Ques 14. Can we get any visitor\'s IP address in Flask? How to get any visitor\'s IP address in Flask?

Yes, we can do it. Request.remoote_addr is useful to get the IP address in Flask. An example is given below:

From flask import request
From flask import jsonify

@app.route(\"/get_user_ip\",method=[\"GET\"]
def get_user_ip():
  return jsonify({\'ip\': request.remote_addr}), 200

Ques 15. Explain Flask error handlers?

Generally, an HTTP error code will be returned when one error comes. Suppose the error code is within 400 to 499; then it is sure that a mistake is happening in the client-side request. Otherwise, if the error code is within 500 to 599, the error comes from a server-side request.

HTTP error code can show custom error pages to the user. This HTTPS error code is not set to the error handler’s code. While returning a message from the error handler, we have to include it.