"[...] I'm using FastAPI a ton these days. [...] I'm actually planning to use it for all of my team's ML services at Microsoft. Some of them are getting integrated into the core Windows product and some Office products."
"Honestly, what you've built looks super solid and polished. In many ways, it's what I wanted Hug to be - it's really inspiring to see someone build that."
$ uvicorn main:app --reloadINFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)INFO: Started reloader process [28720]INFO: Started server process [28722]INFO: Waiting for application startup.INFO: Application startup complete.
About the command uvicorn main:app --reload...
The command uvicorn main:app refers to:
main: the file main.py (the Python "module").
app: the object created inside of main.py with the line app = FastAPI().
--reload: make the server restart after code changes. Only do this for development.
The interactive API documentation will be automatically updated, including the new body:
Click on the button "Try it out", it allows you to fill the parameters and directly interact with the API:
Then click on the "Execute" button, the user interface will communicate with your API, send the parameters, get the results and show them on the screen:
Spoiler alert: the tutorial - user guide includes:
Declaration of parameters from other different places as: headers, cookies, form fields and files.
How to set validation constraints as maximum_length or regex.
A very powerful and easy to use Dependency Injection system.
Security and authentication, including support for OAuth2 with JWT tokens and HTTP Basic auth.
More advanced (but equally easy) techniques for declaring deeply nested JSON models (thanks to Pydantic).
GraphQL integration with Strawberry and other libraries.
Many extra features (thanks to Starlette) as:
WebSockets
extremely easy tests based on requests and pytest
CORS
Cookie Sessions
...and more.
Performance
Independent TechEmpower benchmarks show FastAPI applications running under Uvicorn as one of the fastest Python frameworks available, only below Starlette and Uvicorn themselves (used internally by FastAPI). (*)
To understand more about it, see the section Benchmarks.
tiangolo/fastapi
FastAPI framework, high performance, easy to learn, fast to code, ready for production
Documentation: https://fastapi.tiangolo.com
Source Code: https://github.com/tiangolo/fastapi
FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints.
The key features are:
Fast: Very high performance, on par with NodeJS and Go (thanks to Starlette and Pydantic). One of the fastest Python frameworks available.
Fast to code: Increase the speed to develop features by about 200% to 300%. *
Fewer bugs: Reduce about 40% of human (developer) induced errors. *
Intuitive: Great editor support. Completion everywhere. Less time debugging.
Easy: Designed to be easy to use and learn. Less time reading docs.
Short: Minimize code duplication. Multiple features from each parameter declaration. Fewer bugs.
Robust: Get production-ready code. With automatic interactive documentation.
Standards-based: Based on (and fully compatible with) the open standards for APIs: OpenAPI (previously known as Swagger) and JSON Schema.
* estimation based on tests on an internal development team, building production applications.
Sponsors
Other sponsors
Opinions
"[...] I'm using FastAPI a ton these days. [...] I'm actually planning to use it for all of my team's ML services at Microsoft. Some of them are getting integrated into the core Windows product and some Office products."
"We adopted the FastAPI library to spawn a REST server that can be queried to obtain predictions. [for Ludwig]"
"Netflix is pleased to announce the open-source release of our crisis management orchestration framework: Dispatch! [built with FastAPI]"
"I’m over the moon excited about FastAPI. It’s so fun!"
"Honestly, what you've built looks super solid and polished. In many ways, it's what I wanted Hug to be - it's really inspiring to see someone build that."
"If you're looking to learn one modern framework for building REST APIs, check out FastAPI [...] It's fast, easy to use and easy to learn [...]"
"We've switched over to FastAPI for our APIs [...] I think you'll like it [...]"
Typer, the FastAPI of CLIs
If you are building a CLI app to be used in the terminal instead of a web API, check out Typer.
Typer is FastAPI's little sibling. And it's intended to be the FastAPI of CLIs.⌨️ 🚀
Requirements
Python 3.6+
FastAPI stands on the shoulders of giants:
Installation
You will also need an ASGI server, for production such as Uvicorn or Hypercorn.
Example
Create it
main.py
with:Or use
async def
...If your code uses
async
/await
, useasync def
:Note:
If you don't know, check the "In a hurry?" section about
async
andawait
in the docs.Run it
Run the server with:
About the command
uvicorn main:app --reload
...The command
uvicorn main:app
refers to:main
: the filemain.py
(the Python "module").app
: the object created inside ofmain.py
with the lineapp = FastAPI()
.--reload
: make the server restart after code changes. Only do this for development.Check it
Open your browser at http://127.0.0.1:8000/items/5?q=somequery.
You will see the JSON response as:
You already created an API that:
/
and/items/{item_id}
.GET
operations (also known as HTTP methods)./items/{item_id}
has a path parameteritem_id
that should be anint
./items/{item_id}
has an optionalstr
query parameterq
.Interactive API docs
Now go to http://127.0.0.1:8000/docs.
You will see the automatic interactive API documentation (provided by Swagger UI):
Alternative API docs
And now, go to http://127.0.0.1:8000/redoc.
You will see the alternative automatic documentation (provided by ReDoc):
Example upgrade
Now modify the file
main.py
to receive a body from aPUT
request.Declare the body using standard Python types, thanks to Pydantic.
The server should reload automatically (because you added
--reload
to theuvicorn
command above).Interactive API docs upgrade
Now go to http://127.0.0.1:8000/docs.
Alternative API docs upgrade
And now, go to http://127.0.0.1:8000/redoc.
Recap
In summary, you declare once the types of parameters, body, etc. as function parameters.
You do that with standard modern Python types.
You don't have to learn a new syntax, the methods or classes of a specific library, etc.
Just standard Python 3.6+.
For example, for an
int
:or for a more complex
Item
model:...and with that single declaration you get:
str
,int
,float
,bool
,list
, etc).datetime
objects.UUID
objects.Coming back to the previous code example, FastAPI will:
item_id
in the path forGET
andPUT
requests.item_id
is of typeint
forGET
andPUT
requests.q
(as inhttp://127.0.0.1:8000/items/foo?q=somequery
) forGET
requests.q
parameter is declared with= None
, it is optional.None
it would be required (as is the body in the case withPUT
).PUT
requests to/items/{item_id}
, Read the body as JSON:name
that should be astr
.price
that has to be afloat
.is_offer
, that should be abool
, if present.We just scratched the surface, but you already get the idea of how it all works.
Try changing the line with:
...from:
...to:
...and see how your editor will auto-complete the attributes and know their types:
For a more complete example including more features, see the Tutorial - User Guide.
Spoiler alert: the tutorial - user guide includes:
maximum_length
orregex
.requests
andpytest
Performance
Independent TechEmpower benchmarks show FastAPI applications running under Uvicorn as one of the fastest Python frameworks available, only below Starlette and Uvicorn themselves (used internally by FastAPI). (*)
To understand more about it, see the section Benchmarks.
Optional Dependencies
Used by Pydantic:
ujson
- for faster JSON "parsing".email_validator
- for email validation.Used by Starlette:
requests
- Required if you want to use theTestClient
.jinja2
- Required if you want to use the default template configuration.python-multipart
- Required if you want to support form "parsing", withrequest.form()
.itsdangerous
- Required forSessionMiddleware
support.pyyaml
- Required for Starlette'sSchemaGenerator
support (you probably don't need it with FastAPI).ujson
- Required if you want to useUJSONResponse
.Used by FastAPI / Starlette:
uvicorn
- for the server that loads and serves your application.orjson
- Required if you want to useORJSONResponse
.You can install all of these with
pip install "fastapi[all]"
.License
This project is licensed under the terms of the MIT license.