When it comes to building web applications, developers have a variety of options to choose from. Although Django is the more established choice if you're writing a serious web application in Python, if you're building a smaller or more niche application, it maybe overkill.

Two alternative popular frameworks for building web applications in Python are FastAPI and Flask. Both frameworks offer a simple and lightweight approach to building web applications, but there are some key differences between the two that developers should consider when deciding which one to use.

In this blog post, we will take a comprehensive look at FastAPI and Flask, comparing their advantages, disadvantages, and use cases to help you choose the right web framework for your project.

What is FastAPI?

FastAPI is a modern, fast, and lightweight web framework for building APIs in Python. It is built on top of Starlette, a lightweight ASGI framework, and utilizes the latest Python asyncio features to provide fast and asynchronous request handling. FastAPI is designed to be easy to use and easy to learn, with a minimalistic approach that allows developers to get started quickly.

FastAPI is also notable for its automatic validation and documentation features. It uses OpenAPI and JSON Schema to automatically validate request payloads and generate OpenAPI documentation for your API. This means that you don't have to write your own validation code or manually maintain API documentation, saving you time and effort.

What is Flask?

Flask is a popular web framework for building web applications in Python. It is a minimalistic framework that gives developers a lot of control over the structure and functionality of their application. Flask is easy to get started with, with a small learning curve and a large community of users who have created a wide range of extensions and libraries that can be easily integrated into a Flask application.

Flask is a traditional web framework that has been around for over a decade, and it is used by many developers to build a wide range of web applications, from simple websites to complex web systems.

FastAPI vs. Flask: Advantages

Let's take a look at the main advantages of using FastAPI and Flask for web development.

Advantages of FastAPI

Performance: FastAPI is built on top of an asyncio-based framework, which means that it is well-suited for handling a large number of concurrent requests. This makes FastAPI ideal for building high-performance APIs and applications that need to handle a large amount of traffic.

Automatic validation and documentation: FastAPI uses OpenAPI and JSON Schema to automatically validate request payloads and generate OpenAPI documentation for your API. This saves you time and effort by eliminating the need to write your own validation code or maintain API documentation manually.

Easy to learn and use: FastAPI is designed to be easy to learn and use, with a minimalistic approach that allows developers to get started quickly. It also has excellent documentation and a growing community of users, making it easy to find help and resources when building an application with FastAPI.

Advantages of Flask

Simplicity and flexibility: Flask is a minimalistic framework that gives developers a lot of control over the structure and functionality of their application. This makes it very flexible and easy to customize for specific use cases.

Easy to get started with: Flask has a small learning curve and is easy to get started with, making it a good choice for developers who are new to web development. It also has a large community of users who have created a wide range of extensions and libraries that can be easily integrated into a Flask application.

Established and well-supported: Flask has been around for over a decade and has a large and active community of users and developers. This means that it is well-established and well-supported, with a wealth of resources and documentation available to help developers build their applications.

FastAPI vs. Flask: Disadvantages

While FastAPI and Flask have many advantages, they also have some potential disadvantages that developers should be aware of.

Disadvantages of FastAPI

Relatively new: FastAPI is a relatively new framework compared to Flask, which has been around for over a decade. This means that there is a smaller community of developers using FastAPI, which can make it more difficult to find help or resources when building an application with FastAPI.

Focused on building APIs: FastAPI is primarily designed for building APIs, rather than traditional web applications. While FastAPI can be used to build a full web application, it may not have all of the features and functionality of a more established web framework like Flask.

Disadvantages of Flask

Not as performant: Flask is not built on top of an asyncio-based framework, which means that it may not be well-suited for handling a large number of concurrent requests. This can make Flask less performant than other frameworks, such as FastAPI.

No automatic validation and documentation: Flask does not have automatic validation and documentation features like FastAPI, which means that developers will have to write their own validation code and maintain API documentation manually. This can be time-consuming and error-prone.

FastAPI vs. Flask: Use Cases

Now that we've looked at the advantages and disadvantages of FastAPI and Flask, let's consider some common use cases for each framework.

Use Cases for FastAPI

Building APIs: FastAPI is specifically designed for building APIs, and it excels at this task. Its fast performance and automatic validation and documentation make it a great choice for building high-quality APIs that need to handle a large amount of traffic.

Building high-performance applications: Because of its asyncio-based architecture, FastAPI is well-suited for building high-performance applications that need to handle a large number of concurrent requests. If performance is a key concern for your application, FastAPI may be the right choice.

Use Cases for Flask

Building traditional web applications: Flask is a more traditional web framework that is well-suited for building a wide range of web applications, from simple websites to complex web systems. Its simplicity and flexibility make it a good choice for developers who want a lot of control over the structure and functionality of their application.

Getting started with web development: Flask has a small learning curve and is easy to get started with, making it a good choice for developers who are new to web development. Its large community of users also means that there are plenty of resources and documentation available to help you get started.

Conclusion

In conclusion, both FastAPI and Flask are useful frameworks for building web applications in Python. FastAPI is a newer framework that is focused on building APIs and offers fast performance and automatic validation and documentation. Flask is a more established framework that is more flexible and easy to get started with, but may not be as performant as FastAPI.

Ultimately, the decision of which framework to use will depend on the specific needs and requirements of your application. If you are building an API and performance is a key concern, FastAPI may be the right choice. If you are building a traditional web application and need more flexibility and control, Flask may be the better option.