Designing Web Applications with Python and Flask

For which projects is Flask best and for which Django? What features of Flask can be used most effectively when developing web applications? I am Alexey Nekrasov, leader of the Python direction at MTS, author of the library fork flask-combo-jsonapiprogram director of Python courses at Skillbox, CEO Forkway and the author of the channel Python – learn and work.

Today, perhaps, no one writes web applications in Python anymore. I mean “pure” Python: developers have convenient web frameworks at their disposal that significantly speed up and simplify this process. One of them is Flask.

Flask vs Django

When we talk about frameworks for creating web applications in Python, Django is the first to come to mind; Flask is not immediately remembered. Indeed, Flask and Django are two synchronous web frameworks; besides them, many developers prefer FastAPI because of its asynchrony and speed. If we conduct a small analysis of vacancies on hh.ru related to web development in Python, we will see that in 44% of cases candidates are expected to know Django, in 25% – Flask, and 31% of employers indicate FastAPI in their requirements. However, when we are faced with the task of choosing a technology for our own pet project, we, of course, need to focus not on the job market, but on the capabilities of the framework, its characteristic features and our knowledge. Let’s say you’ve learned the basic Python syntax and want to quickly develop a web service to solve some application problem. You’ve heard about asynchronous Python, but you don’t know how it works, and you need the service tomorrow. In this case, existing knowledge and skills somewhat limit the choice.

So why is Django so popular? There are many reasons for this, but the main one is that Django can be classified as a “batteries included” product—that is, it provides a lot of useful tools and features out of the box. Two more undoubted advantages are scalability (Django is good for large projects) and security: this framework pays significant attention to protection against threats. Finally, Django boasts a large developer community that provides extensive support for the project and also creates a significant number of useful plugins and add-ons.

Advantages of Flask

Firstly, it is lightweight: yes, the framework provides a minimal set of tools, but it allows you to quickly start development, which is very important for small applications. Secondly, Flask is ideal for creating microservices. If the application is built on the basis of a microservice architecture, it is much easier to implement it using Flask. Additionally, Flask is great for creating lightweight APIs. If you are familiar only with Python syntax and need to quickly integrate your project with other web applications or ensure its interaction with an existing API, this framework is an excellent choice for solving the problem. So, Flask makes sense to choose for the following reasons:

  • lightness: Flask allows you to quickly create small web applications;

  • microservices: Flask is ideal for creating microservice architectures;

  • API: Flask easily integrates with extensions to create APIs;

  • Jinja2 template engine: Powerful and flexible engine for web page layout;

  • ORM independence: Flask gives you the freedom to choose your ORM.

So that everything said above does not look like unfounded statements, let’s look at several practical cases to understand in which situations it is better to use Flask and in which Django. Let’s list the advantages and disadvantages of these frameworks for each case we mentioned.

Case 1: Checking server operation via API

Flask

Pros:

  • Fast start. Creating a basic API in Flask requires just a few lines of code.

  • Simplicity and lightness. There are no unnecessary dependencies or settings.

Minuses:

Django:

Pros:

  • More functionality out of the box, for example the presence of an administration panel (in this case it is not needed).

  • Built-in authentication system.

Minuses:

For simple server testing using the API, Flask would be a better choice due to its simplicity and speed of deployment.

Case 2: Creating a marketplace

Flask:

Pros:

  • Flexibility. The choice of application components and structure is entirely in the hands of the developer.

  • Lightness. You can add only those components that are really needed.

Minuses:

  • May require more development time due to the need to integrate additional extensions.

  • The risk of “spaghetti code” appearing in the absence of a clear project structure.

Django:

Pros:

  • Fast development thanks to many built-in tools.

  • A clear project structure reduces the risk of spaghetti code.

  • Built-in authentication system and admin panel.

Minuses:

For creating a marketplace, Django is the preferred choice due to its wide range of out-of-the-box features and clear structure, which speeds up development and reduces the risk of creating spaghetti code.

So, let’s summarize the preliminary results. Which web applications make sense to develop using Flask, and which ones shouldn’t?

Types of applications that can be created with Flask:

  • API: Flask is ideal for creating RESTful APIs due to the lightweight and flexible framework.

  • Single Page Applications (SPAs): You can develop both backend and frontend for SPA in Flask (using Jinja2).

  • Microservices: Due to its lightweight nature, Flask is often used to create microservices.

  • Blogs, CMS and other traditional web applications.

  • Prototyping: Rapid prototyping to demonstrate ideas or features.

Types of applications that are not recommended to be created in Flask (primarily due to high complexity):

  • Large and complex web applications: Such applications may require a more powerful framework such as Django, which provides more built-in tools and features.

  • E-commerce: While it is possible to create an online store with Flask, there are other frameworks and platforms specifically designed for e-commerce.

  • High load applications: Flask may require additional optimization and tuning to handle large numbers of requests per second.

Where can I host Flask applications?

Flask applications can be hosted on almost any hosting that supports Python. This category includes cloud platforms, such as Yandex Cloud, Heroku, as well as traditional VPS and other hosting. For development and testing, Flask typically uses the built-in Werkzeug server. However, for production it is recommended to use more powerful servers such as Gunicorn, uWSGI or mod_wsgi in combination with servers like Nginx or Apache.

Please note that Flask requires Python version 3.5 or higher. Additional libraries and extensions may also be required depending on the functionality of the applications being developed.

Application development cycle and features of Flask

The backend of applications implemented in Flask has a number of characteristic architectural features that affect the process and development cycle. Firstly, this modularity: Flask supports dividing your application into modules, or blueprints, to better organize your code. Secondly, the framework allows you to create a separate file or module for storing and changing application settings. Third, extensibility: Flask makes it easy to integrate third-party extensions, but you should think about this in advance, preferably before the development cycle begins.

Before you start creating an application in Flask (as well as in any other framework), you need to go through a number of preparatory steps, which I have listed below.

  1. Definition of requirements: clearly define functional and non-functional requirements for the backend part of the application.

  2. Application structure design: identify the main components, modules and their interactions.

  3. Designing database models: think over the data structure, relationships between tables and indexes.

  4. API design: Define methods, endpoints, and response formats for interacting with the frontend and other consumers of your API.

  5. Tool selection: Consider what additional libraries and tools will be used (eg databases, queuing systems).

  6. Environment setup: install Python, Flask and other necessary tools. Set up your virtual environment.

Now you can start directly developing. The cycle of creating a web application using Flask includes 5 stages:

  1. Planning: defining requirements, designing architecture, database models and APIs – I listed these preparatory stages above.

  2. Development: writing code directly.

  3. Testing: checking the application for errors and inconsistencies with requirements.

  4. Deploy: deploying the application on a server or in the cloud.

  5. Monitoring and support: tracking bugs, performance and making necessary changes.

If the importance of the first point is generally obvious – without proper planning, the development process risks very quickly turning into chaos – and the next three are self-explanatory, then I would like to dwell on the last point in a little more detail.

Features of support and testing

What do we do first when a web application crashes or something suddenly falls off for no apparent reason? Right, we burn out we read the logs. Therefore, proper organization of logging is an extremely important task.

Flask uses the standard Python library for logging. You can easily configure logging so that messages at different levels are saved to files, streams, or remote logging systems such as Logstash or Graylog. In addition, you can choose the external library loguru, it is quite well configured out of the box. Third-party extensions such as Flask-Logging can provide additional capabilities, and Sentry integration is fully supported.

To debug a web application, the built-in debugger is used, which provides useful information about errors during the development process. The main thing in production is to remember to turn it off! Also, many IDEs have built-in debuggers; they close about 95% of cases.

Flask supports unit testing using the standard unittest library, but I prefer pytest for this purpose. The framework’s architecture also includes a special FlaskClient class for testing applications at the request level.

Community

As the famous children’s song says, it’s fun to walk through the open spaces together. And developing large and complex web applications is even more fun. The same notorious Django has a very large community that is engaged in both development and support. What about Flask?

Flask has one of the most active communities among Python web frameworks. There is also extensive documentation for Flask, available in English. It covers all aspects of using this framework – from basic principles to advanced topics.

Thanks to an active community, there are many extensions and plugins for Flask that add additional functionality and integrations. There are many forums, groups and communities where developers can discuss Flask-related issues, the liveliest ones can be found on Stack Overflow and Reddit. Here are some links to useful resources for Flask developers that are best to have on hand just in case.

  1. Official Flask documentation (en).

  2. Flask on GitHub — source code, problems and discussions.

  3. List of extensions for Flask (en).

  4. Awesome Flask — A curated list of useful libraries, resources and training materials.

  5. Mega-Tutorial Flask (en) – An extensive guide to creating a complete web application in Flask.

  6. Python – learn and work (ru) — a Telegram channel where I talk about development, including Flask.

  7. Python Flask (en) — community group on Telegram.

Conclusion

Flask is a flexible and powerful framework with an active community that is suitable for solving a wide range of web development problems. Yes, on course Python developer In Skillbox, the framework is taught using the example of developing the server part of a social network. Simplicity and flexibility make Flask an ideal choice for custom projects and rapid iteration, while extensive resources and community support ensure high-quality application development and scaling.

It’s important to remember, as with any tool, that the choice between Flask and other frameworks such as Django should be based on the specific requirements and goals of your project. Flask is just a technology that has a very wide, but still limited range of applications.

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