This repository gives a small overview and comparison for both Flask and FastAPI.
Table of Content:
poetry installAfter the installation, you can start the FastAPI backend via:
poe start-fastapiYou can open the OpenAPI definition in http://127.0.0.1:8000/docs.
After the installation, you can start the Flask backend via:
poe start-flask| Flask | FastAPI |
|---|---|
| 2010 | 2019 |
| Micro framework | Full-Stack framwork |
| Async support from > v2.0 | Async first |
| License: BSD-3 Clause | License: MIT |
| No built-in data validation | Built-in data validation with pydantic |
| Out-of-the-box OpenAPI documentation |
Apparently, there are a few discussions online regarding the speed of both frameworks. Initially, FastAPI was supposed to be the faster framework due to the async-first implementation. However, with version 2.0, Flask also added async support:
- https://www.reddit.com/r/flask/comments/xvw1vi/misunderstandings_about_how_async_works_with/
- https://www.reddit.com/r/flask/comments/13pyxie/flask_vs_fastapi/
- https://stackoverflow.com/questions/76297879/benchmarks-of-fastapi-vs-async-flask
- https://flask.palletsprojects.com/en/2.3.x/async-await/
- https://blog.miguelgrinberg.com/post/ignore-all-web-performance-benchmarks-including-this-one
- https://www.geeksforgeeks.org/flask-vs-fastapi/
Similarly, there are also some open discussions whether one should always define routes in FastAPI with async
or not:
- https://www.reddit.com/r/FastAPI/comments/18c66xt/how_do_you_decide_which_functionsroutes_should_be/
- https://christophergs.com/tutorials/ultimate-fastapi-tutorial-pt-9-asynchronous-performance-basics/
- https://rishibajargan.medium.com/do-not-over-use-async-with-fastapi-fa70bed14d9c
- fastapi/fastapi#10771
- https://superfastpython.com/asyncio-vs-threading/
- https://www.geeksforgeeks.org/blocking-and-nonblocking-io-in-operating-system/
For normal path operation functions (without async), the function is run in an external threadpool that is then
awaited, instead of being called directly (See: documentation).
The only official answer (discussion 10771) states:
FastAPI is an async framework, and async should the be the default choice.
and that the "threadpool def endpoints" are merely an escape hatch.