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

Documentation:https://fastapi.tiangolo.com

Source Code:https://github.com/fastapi/fastapi

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 withNodeJS andGo (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.

Other sponsors

"[...] I'm usingFastAPI a 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 coreWindows product and someOffice products."

"We adopted theFastAPI library to spawn aREST server that can be queried to obtainpredictions. [for Ludwig]"

"Netflix is pleased to announce the open-source release of ourcrisis management orchestration framework:Dispatch! [built withFastAPI]"

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

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

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

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

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

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

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

FastAPI stands on the shoulders of giants:

• Starlette for the web parts.
• Pydantic for the data parts.

Create and activate avirtual environment and then install FastAPI:

$pip install"fastapi[standard]"---> 100%

Note: Make sure you put"fastapi[standard]" in quotes to ensure it works in all terminals.

Create a filemain.py with:

fromtypingimportUnionfromfastapiimportFastAPIapp=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}

fromtypingimportUnionfromfastapiimportFastAPIapp=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}

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 WatchFilesINFO:     Started server process [2248757]INFO:     Waiting for application startup.INFO:     Application startup complete.

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}.
• Bothpaths takeGEToperations (also known as HTTPmethods).
• Thepath/items/{item_id} has apath parameteritem_id that should be anint.
• Thepath/items/{item_id} has an optionalstrquery parameterq.

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

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

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

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

Now modify the filemain.py to receive a body from aPUT request.

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

fromtypingimportUnionfromfastapiimportFastAPIfrompydanticimportBaseModelapp=FastAPI()classItem(BaseModel):name:strprice:floatis_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 dev server should reload automatically.

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:

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

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

In summary, you declareonce 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 standardPython.

For example, for anint:

item_id:int

or for a more complexItem model:

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).
  • datetime objects.
  • UUID objects.
  • Database models.
  • ...and many more.
• Automatic interactive API documentation, including 2 alternative user interfaces:
  • Swagger UI.
  • ReDoc.

Coming back to the previous code example,FastAPI will:

• Validate that there is anitem_id in the path forGET andPUT requests.
• Validate that theitem_id is of typeint forGET andPUT requests.
  • 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) forGET requests.
  • As theq parameter is declared with= None, it is optional.
  • Without theNone it would be required (as is the body in the case withPUT).
• ForPUT requests to/items/{item_id}, read the body as JSON:
  • Check that it has a required attributename that should be astr.
  • Check that it has a required attributeprice that 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.

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 ofparameters from other different places as:headers,cookies,form fields andfiles.
• How to setvalidation constraints asmaximum_length orregex.
• A very powerful and easy to useDependency Injection system.
• Security and authentication, including support forOAuth2 withJWT tokens andHTTP Basic auth.
• More advanced (but equally easy) techniques for declaringdeeply nested JSON models (thanks to Pydantic).
• GraphQL integration withStrawberry and other libraries.
• Many extra features (thanks to Starlette) as:
  • WebSockets
  • extremely easy tests based on HTTPX andpytest
  • CORS
  • Cookie Sessions
  • ...and more.

Independent TechEmpower benchmarks showFastAPI applications 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.

FastAPI depends on Pydantic and Starlette.

When you install FastAPI withpip install "fastapi[standard]" it comes with thestandard group of optional dependencies:

Used by Pydantic:

• email-validator - for email validation.

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:

• uvicorn - for the server that loads and serves your application. This includesuvicorn[standard], which includes some dependencies (e.g.uvloop) needed for high performance serving.
• fastapi-cli[standard] - to provide thefastapi command.
  • This includesfastapi-cloud-cli, which allows you to deploy your FastAPI application toFastAPI Cloud.

If you don't want to include thestandard optional dependencies, you can install withpip install fastapi instead ofpip install "fastapi[standard]".

If you want to install FastAPI with the standard dependencies but without thefastapi-cloud-cli, you can install withpip install "fastapi[standard-no-fastapi-cloud-cli]".

There are some additional dependencies you might want to install.

Additional optional Pydantic dependencies:

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

Additional optional FastAPI dependencies:

• orjson - Required if you want to useORJSONResponse.
• ujson - Required if you want to useUJSONResponse.

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