Flask Interview Questions and Answers

Ques 1. What is Flask?

Flask is a Python-based framework that builds web applications. The interface is mostly based on HTTP, REST, GraphQL, or Websockets. This framework is based on the Jinja2 templates engine and WSGI web application library. The creator, Armin Ronacher, developed it for the Pallets project initially.

Ques 2. Is Flask an open-source framework?

Yes, Flask is an open-source framework.

Ques 3. Why do we use the Flask framework in web application development?

Flask framework is based on the Python programming language. It has a quick microframework based on prototyping web and networking applications to execute the code faster. We can use Flask in the below-mentioned cases:

1. When we need to develop an API or ML Model.
2. To control security camera by API abstraction.
3. When we need to work on no-SQL like DynamoDB.
4. When we need to do ElasticSearch.
5. When we need to prepare a microservice adapter to translate SOAP API into JSON.

Ques 4. How can we download the Flask development version?

We can get the Flask development version by using the given below command:

git clone https://github.com/pallets/flask
cd flask && python3 setup.py develop

Ques 5. How to install Flask in Linux?

You can install Flask in a Linux environment using Python package manager, pip.

Ques 6. What is the default local host and port in Flask?

The default Flask local host is 127.0.0.1 and the default port is 5000.

Ques 7. How can we get a string in Flask?

We can get the string by using the argument's value. This value will be used as the request object in Flask.

For example, we can try this sample code:

from flask import Flask
from flask import request
app=Flask(_name_)
@app.route(“/”)
def index():
  val=request.args.get(“var”)
  return “Hello,World {}”
  if_name_==”_main_”:
    app.run(host=”0.0.0.0”,port=8080)

Ques 8. Why is Flask famous as a microframework?

It has some core features like requests, routing, and blueprints, as well as a few other features like coaching, ORM, and forms. Because of all these features, we call Flask a microframework.

Ques 9. Wwhy we need to use Flask, not Django?

Flask is a better quick development Python framework. It uses cases and perfects prototyping. It is better for lightweight web applications. It is best to develop microservice and server-less applications. In comparison, it has full features that are built-in. Flask is also easy to learn with so many APIs. In Django, there are fewer APIs.

Ques 10. What is the application context in Flask?

It is the basic idea to complete the response circle in the Flask application. During any request of the CLI command, it maintains all track of application-level data. We can use g object or current _app to access those data. Always Flask forced application context with every request to complete the circle.

Ques 11. How to create the RESTFul application in the Flask framework?

There are so many extensions that we can use to create the RESTFul application in Flask. We need to choose them depending upon the requirements.

A few of them are as follows:

1. Flask-RESTFul.
2. Flask-API.
3. Flask-RESTX.
4. Connexion.

Ques 12. How to create an admin interface in Flask?

Here we also need to use one of the Flask extensions named Flask-Admin. It helps to group all individual views together in classes. Another extension named Flask-Appbuilder can be used. It has a built-in admin interface.

Ques 13. How to debug a Flask application?

We can debug the Flask application. Every development server has a debugging facility. Flask also comes with one server, so one server is there by default. If we run the method to call the Flask application object, we need to keep the debug mode value true. 

Remember that we need to deactivate the debug mode before deploying; otherwise, a full stack trace will be displayed in a browser. It is not secure as it has confidential details. One extension is also available named Flask-DebugToolbar.

Ques 14. Tell about the identifiers in Flask.

Actually, it can be any length. But there are certain rules which we must follow:

1. The identifier should start with a  character or an underscore, or from A-Z or a-z.
2. A-Z or a-z can be stored as a name in the identifier.
3. Python Flask is case-sensitive.
4. Few keywords are not usable in identifiers like and, false, import, true, del, try, etc.

Ques 15. How many HTTP methods can we use in Flask?

Basically, we use 5 types of HTTP methods to retrieve data from URLs. They are:

1. GET: It sends the unencrypted data to the server.
2. POST: Post server caches all data except HTML.
3. HEAD: It is similar to GET without any response body.
4. PUT: It can replace current data.
5. DELETE: It can delete the current data requested by any URL.

Ques 16. Is Flask an MVC framework?

Yes, it is an MVC( Model View Control) framework. Because it has a feature named session, this helps to remember information from one request to another request. It uses a signed cookie to show the contents of that session to the user. If the user wants to modify. They have to use one secret key named Flask.secret_key in Flask. Flask perfectly behaves like one MVC framework.

Ques 17. How to show all errors in the browser for Flask?

We need to run Python files on the shell. The command will be app.debug=True

Ques 18. What type of Applications can we create with Flask?

With Flask, we can create almost all types of web applications. We can create Single Page Application, RESTful API based Applications, SAS applications, Small to medium size websites, static websites, Microservices, and serverless apps.

Flask is so versatile and flexible as it can be integrated with other technologies very quickly to achieve the same. 

For example, Flask can be combined with the NodeJS serverless, AWS lambda, and similar other third party services to build new-age systems.