FastAPI framework, high performance, easy to learn, fast to code, ready for production

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Documentation:https://fastapi.tiangolo

Source Code:https://github /tiangolo/fastapi

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FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.

The key features are:

• Fast:Very high performance, on par withNodeJSandGo(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) andJSON Schema.

* estimation based on tests on an internal development team, building production applications.

Sponsors

Other sponsors

Opinions

"[...] I'm usingFastAPIa ton these days. [...] I'm actually planning to use it for all of my team'sML services at Microsoft.Some of them are getting integrated into the coreWindowsproduct and someOfficeproducts."

Kabir Khan -Microsoft(ref)

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"We adopted theFastAPIlibrary to spawn aRESTserver that can be queried to obtainpredictions.[for Ludwig]"

Piero Molino, Yaroslav Dudin, and Sai Sumanth Miryala -Uber(ref)

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"Netflixis pleased to announce the open-source release of ourcrisis managementorchestration framework:Dispatch![built withFastAPI]"

Kevin Glisson, Marc Vilanova, Forest Monsen -Netflix(ref)

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"I’m over the moon excited aboutFastAPI.It’s so fun!"

Brian Okken -Python Bytespodcast host(ref)

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"Honestly, what you've built looks super solid and polished. In many ways, it's what I wantedHugto be - it's really inspiring to see someone build that."

Timothy Crosley -Hugcreator(ref)

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"If you're looking to learn onemodern frameworkfor building REST APIs, check outFastAPI[...] It's fast, easy to use and easy to learn [...]"

"We've switched over toFastAPIfor ourAPIs[...] I think you'll like it [...]"

Ines Montani - Matthew Honnibal -Explosion AIfounders -spaCycreators(ref)-(ref)

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"If anyone is looking to build a production Python API, I would highly recommendFastAPI.It isbeautifully designed,simple to useandhighly scalable,it has become akey componentin our API first development strategy and is driving many automations and services such as our Virtual TAC Engineer."

Deon Pillsbury -Cisco(ref)

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Typer,the FastAPI of CLIs

If you are building a CLI app to be used in the terminal instead of a web API, check outTyper.

Typeris FastAPI's little sibling. And it's intended to be theFastAPI of CLIs.⌨️ 🚀

Requirements

FastAPI stands on the shoulders of giants:

• Starlettefor the web parts.
• Pydanticfor the data parts.

Installation

$pip install fastapi

---> 100%

Example

Create it

• Create a filemain.pywith:

fromtypingimportUnion

fromfastapiimportFastAPI

app=FastAPI()


@app.get("/")
defread_root():
return{"Hello":"World"}


@app.get("/items/{item_id}")
defread_item(item_id:int,q:Union[str,None]=None):
return{"item_id":item_id,"q":q}

Or useasync def...

If your code usesasync/await,useasync def:

fromtypingimportUnion

fromfastapiimportFastAPI

app=FastAPI()


@app.get("/")
asyncdefread_root():
return{"Hello":"World"}


@app.get("/items/{item_id}")
asyncdefread_item(item_id:int,q:Union[str,None]=None):
return{"item_id":item_id,"q":q}

Note:

If you don't know, check the"In a hurry?"section aboutasyncandawaitin the docs.

Run it

Run the server with:

$fastapi dev main.py

╭────────── FastAPI CLI - Development mode ───────────╮
│ │
│ Serving at: http://127.0.0.1:8000 │
│ │
│ API docs: http://127.0.0.1:8000/docs │
│ │
│ Running in development mode, for production use: │
│ │
│ fastapi run │
│ │
╰─────────────────────────────────────────────────────╯

INFO: Will watch for changes in these directories: ['/home/user/code/awesomeapp']
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: Started reloader process [2248755] using WatchFiles
INFO: Started server process [2248757]
INFO: Waiting for application startup.
INFO: Application startup complete.

About the commandfastapi dev main.py...

The commandfastapi devreads yourmain.pyfile, detects theFastAPIapp in it, and starts a server usingUvicorn.

By default,fastapi devwill start with auto-reload enabled for local development.

You can read more about it in theFastAPI CLI docs.

Check it

Open your browser athttp://127.0.0.1:8000/items/5?q=somequery.

You will see the JSON response as:

{"item_id":5,"q":"somequery"}

You already created an API that:

• Receives HTTP requests in thepaths/and/items/{item_id}.
• BothpathstakeGEToperations(also known as HTTPmethods).
• Thepath/items/{item_id}has apath parameteritem_idthat should be anint.
• Thepath/items/{item_id}has an optionalstrquery parameterq.

Interactive API docs

Now go tohttp://127.0.0.1:8000/docs.

You will see the automatic interactive API documentation (provided bySwagger UI):

Alternative API docs

And now, go tohttp://127.0.0.1:8000/redoc.

You will see the alternative automatic documentation (provided byReDoc):

Example upgrade

Now modify the filemain.pyto receive a body from aPUTrequest.

Declare the body using standard Python types, thanks to Pydantic.

fromtypingimportUnion

fromfastapiimportFastAPI
frompydanticimportBaseModel

app=FastAPI()


classItem(BaseModel):
name:str
price:float
is_offer:Union[bool,None]=None


@app.get("/")
defread_root():
return{"Hello":"World"}


@app.get("/items/{item_id}")
defread_item(item_id:int,q:Union[str,None]=None):
return{"item_id":item_id,"q":q}


@app.put("/items/{item_id}")
defupdate_item(item_id:int,item:Item):
return{"item_name":item.name,"item_id":item_id}

Thefastapi devserver should reload automatically.

Interactive API docs upgrade

Now go tohttp://127.0.0.1:8000/docs.

• 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:

Alternative API docs upgrade

And now, go tohttp://127.0.0.1:8000/redoc.

• The alternative documentation will also reflect the new query parameter and body:

Recap

In summary, you declareoncethe 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 standardPython.

For example, for anint:

item_id:int

or for a more complexItemmodel:

item:Item

...and with that single declaration you get:

• Editor support, including:
  • Completion.
  • Type checks.
• Validation of data:
  • Automatic and clear errors when the data is invalid.
  • Validation even for deeply nested JSON objects.
• Conversion of input data: coming from the network to Python data and types. Reading from:
  • JSON.
  • Path parameters.
  • Query parameters.
  • Cookies.
  • Headers.
  • Forms.
  • Files.
• Conversion of output data: converting from Python data and types to network data (as JSON):
  • Convert Python types (str,int,float,bool,list,etc).
  • datetimeobjects.
  • UUIDobjects.
  • Database models.
  • ...and many more.
• Automatic interactive API documentation, including 2 alternative user interfaces:
  • Swagger UI.
  • ReDoc.

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Coming back to the previous code example,FastAPIwill:

• Validate that there is anitem_idin the path forGETandPUTrequests.
• Validate that theitem_idis of typeintforGETandPUTrequests.
  • If it is not, the client will see a useful, clear error.
• Check if there is an optional query parameter namedq(as inhttp://127.0.0.1:8000/items/foo?q=somequery) forGETrequests.
  • As theqparameter is declared with= None,it is optional.
  • Without theNoneit would be required (as is the body in the case withPUT).
• ForPUTrequests to/items/{item_id},Read the body as JSON:
  • Check that it has a required attributenamethat should be astr.
  • Check that it has a required attributepricethat has to be afloat.
  • Check that it has an optional attributeis_offer,that should be abool,if present.
  • All this would also work for deeply nested JSON objects.
• Convert from and to JSON automatically.
• Document everything with OpenAPI, that can be used by:
  • Interactive documentation systems.
  • Automatic client code generation systems, for many languages.
• Provide 2 interactive documentation web interfaces directly.

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We just scratched the surface, but you already get the idea of how it all works.

Try changing the line with:

return{"item_name":item.name,"item_id":item_id}

...from:

..."item_name":item.name...

...to:

..."item_price":item.price...

...and see how your editor will auto-complete the attributes and know their types:

For a more complete example including more features, see theTutorial - User Guide.

Spoiler alert:the tutorial - user guide includes:

• Declaration ofparametersfrom other different places as:headers,cookies,form fieldsandfiles.
• How to setvalidation constraintsasmaximum_lengthorregex.
• A very powerful and easy to useDependency Injectionsystem.
• Security and authentication, including support forOAuth2withJWT tokensandHTTP Basicauth.
• More advanced (but equally easy) techniques for declaringdeeply nested JSON models(thanks to Pydantic).
• GraphQLintegration withStrawberryand other libraries.
• Many extra features (thanks to Starlette) as:
  • WebSockets
  • extremely easy tests based on HTTPX andpytest
  • CORS
  • Cookie Sessions
  • ...and more.

Performance

Independent TechEmpower benchmarks showFastAPIapplications running under Uvicorn asone of the fastest Python frameworks available,only below Starlette and Uvicorn themselves (used internally by FastAPI). (*)

To understand more about it, see the sectionBenchmarks.

Dependencies

Used by Pydantic:

• email_validator- for email validation.
• pydantic-settings- for settings management.
• pydantic-extra-types- for extra types to be used with Pydantic.

Used by Starlette:

• httpx- 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().

Used by FastAPI / Starlette:

• uvicorn- for the server that loads and serves your application.
• orjson- Required if you want to useORJSONResponse.
• ujson- Required if you want to useUJSONResponse.
• fastapi-cli- to provide thefastapicommand.

When you installfastapiit comes these standard dependencies.

fastapi-slim

If you don't want the extra standard optional dependencies, installfastapi-sliminstead.

When you install with:

pip install fastapi

...it includes the same code and dependencies as:

pip install"fastapi-slim[standard]"

The standard extra dependencies are the ones mentioned above.

License

This project is licensed under the terms of the MIT license.