Pros and Cons of Flask and FastAPI (When to Use Each?)

Python microframeworks.

Whenever someone mentions this, the first thing that typically comes to mind for the speaker — if they are a developer — is Flask and FastAPI. This is because both are useful for creating small-scale data science web applications.

But which micro-framework should one use? Flask or FastAPI? Because both libraries offer similar features. Before discussing the pros and cons, let’s see what Flask and FastAPI are.

Flask is a web framework designed for creating web applications. It was developed by Armin Ronacher due to dissatisfaction with Bottle. Moreover, it doesn’t have ORM. Additionally, it is built on the Werkzeug toolkit and Jinja2 templating engine. This is what helps in creating lightweight web applications that have lower resource consumption.

Some pros of using Flask include:

1. Easiness — Although Flask has its syntax and jargon, it is relatively easy to understand compared to other frameworks.
2. Unit Testing — Flask supports unit testing. This helps developers in simulating different conditions for testing code.
3. Development Server — Flask provides a built-in development server. The best part? You can test your applications without deploying them into production.
4. Extend Functionality — Instead of just building an app from scratch, Flask helps you to improve the functionality of an existing app.
5. High Scalability — Flask is highly scalable. This means that even if you have a large app, you don’t need to worry about scalability.

However, like any other microframework, Flask has its cons. For instance, Flask lacks standardization, has limited tools, operates as a single-threaded system, and lacks out-of-the-box support for session management. Not only this, it can potentially have security vulnerabilities due to modules.

Now, what is FastAPI? FastAPI is also a micro-framework used for Python web development. It is also compatible with any database. Companies such as Netflix, Uber, and Zillow use FastAPI. The pros of FastAPI include:

1. Speed — FastAPI has a higher speed than Flask. In fact, it is one of the fastest web frameworks.
2. Concurrency Simplification — FastAPI simplifies concurrency by reducing the need for an event loop and async/await management.
3. Dependency Injection — Because of this, it becomes easy to make changes in code — classes aren’t directly dependent.
4. Built-in Documentation — FastAPI includes built-in documentation. This comes in handy when it comes to explaining software to others.
5. Built-in Validation — FastAPI provides built-in validation. This helps in reducing the need for external validation tools. Result? More concise code.

However, like any other microframework, FastAPI has its cons. For instance, it is not secure. The developer community is also small. However, this will change in the coming years.

So, which should you use? It depends entirely on your needs. If you require fast performance for asynchronous tasks and applications with high concurrency, FastAPI is the way to go. However, if you are a beginner seeking simplicity and flexibility, Flask would be more suitable.