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FastAPI

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

Test Coverage Package version Supported Python versions

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:

* 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."

Kabir Khan - Microsoft (ref)

"We adopted the FastAPI library to spawn a REST server that can be queried to obtain predictions. [for Ludwig]"

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

"Netflix is pleased to announce the open-source release of our crisis management orchestration framework: Dispatch! [built with FastAPI]"

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

"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."

Timothy Crosley - Hug creator (ref)

"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 [...]"

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

Deon Pillsbury - Cisco (ref)

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

FastAPI stands on the shoulders of giants:

Installation

Create and activate a virtual 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.

Example

Create it

from typing import Union

from fastapi import FastAPI

app = FastAPI()

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

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

Or use async def...

If your code uses async / await, use async def:

from typing import Union

from fastapi import FastAPI

app = FastAPI()

@app.get("/") async def read_root(): return {"Hello": "World"}

@app.get("/items/{item_id}") async def read_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 about async and await in 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 command fastapi dev main.py...

The command fastapi dev reads your main.py file, detects the FastAPI app in it, and starts a server using Uvicorn.

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

You can read more about it in the FastAPI CLI docs.

Check it

Open your browser at http://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:

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):

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):

ReDoc

Example upgrade

Now modify the file main.py to receive a body from a PUT request.

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

from typing import Union

from fastapi import FastAPI from pydantic import BaseModel

app = FastAPI()

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

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

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

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

The fastapi dev server should reload automatically.

Interactive API docs upgrade

Now go to http://127.0.0.1:8000/docs.

Swagger UI

Swagger UI interaction

Swagger UI interaction

Alternative API docs upgrade

And now, go to http://127.0.0.1:8000/redoc.

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.

For example, for an int:

item_id: int

or for a more complex Item model:

item: Item

...and with that single declaration you get:

Coming back to the previous code example, FastAPI will:

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:

editor support

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

Spoiler alert: the tutorial - user guide includes:

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.

Dependencies

FastAPI depends on Pydantic and Starlette.

standard Dependencies

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

Used by Pydantic:

Used by Starlette:

Used by FastAPI / Starlette:

Without standard Dependencies

If you don't want to include the standard optional dependencies, you can install with pip install fastapi instead of pip install "fastapi[standard]".

Additional Optional Dependencies

There are some additional dependencies you might want to install.

Additional optional Pydantic dependencies:

Additional optional FastAPI dependencies:

License

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