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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/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](#performance). * **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 {% if sponsors %} {% for sponsor in sponsors.gold -%}

{% endfor -%} {%- for sponsor in sponsors.silver -%}

{% endfor %} {% endif %} 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!_"

Brian Okken - Python Bytes podcast host (ref)

--- "_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 [...]_"

Ines Montani - Matthew Honnibal - Explosion AI founders - spaCy creators (ref) - (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 Python 3.6+ FastAPI stands on the shoulders of giants: * Starlette for the web parts. * Pydantic for the data parts. ## Installation

```console $ pip install fastapi ---> 100% ```

You will also need an ASGI server, for production such as Uvicorn or Hypercorn.

```console $ pip install uvicorn[standard] ---> 100% ```

## Example ### Create it * Create a file `main.py` with: ```Python from typing import Optional 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: Optional[str] = None): return {"item_id": item_id, "q": q} ```

Or use async def...

If your code uses `async` / `await`, use `async def`: ```Python hl_lines="9 14" from typing import Optional 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: Optional[str] = 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:

```console $ uvicorn main:app --reload INFO: 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.

### Check it Open your browser at http://127.0.0.1:8000/items/5?q=somequery. You will see the JSON response as: ```JSON {"item_id": 5, "q": "somequery"} ``` You already created an API that: * Receives HTTP requests in the _paths_ `/` and `/items/{item_id}`. * Both _paths_ take `GET` operations (also known as HTTP _methods_). * The _path_ `/items/{item_id}` has a _path parameter_ `item_id` that should be an `int`. * The _path_ `/items/{item_id}` has an optional `str` _query parameter_ `q`. ### 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](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png) ### 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](https://fastapi.tiangolo.com/img/index/index-02-redoc-simple.png) ## 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. ```Python hl_lines="4 9-12 25-27" from typing import Optional from fastapi import FastAPI from pydantic import BaseModel app = FastAPI() class Item(BaseModel): name: str price: float is_offer: Optional[bool] = None @app.get("/") def read_root(): return {"Hello": "World"} @app.get("/items/{item_id}") def read_item(item_id: int, q: Optional[str] = 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 server should reload automatically (because you added `--reload` to the `uvicorn` command above). ### Interactive API docs upgrade Now go to http://127.0.0.1:8000/docs. * The interactive API documentation will be automatically updated, including the new body: ![Swagger UI](https://fastapi.tiangolo.com/img/index/index-03-swagger-02.png) * Click on the button "Try it out", it allows you to fill the parameters and directly interact with the API: ![Swagger UI interaction](https://fastapi.tiangolo.com/img/index/index-04-swagger-03.png) * 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: ![Swagger UI interaction](https://fastapi.tiangolo.com/img/index/index-05-swagger-04.png) ### Alternative API docs upgrade And now, go to http://127.0.0.1:8000/redoc. * The alternative documentation will also reflect the new query parameter and body: ![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png) ### 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`: ```Python item_id: int ``` or for a more complex `Item` model: ```Python 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 an `item_id` in the path for `GET` and `PUT` requests. * Validate that the `item_id` is of type `int` for `GET` and `PUT` requests. * If it is not, the client will see a useful, clear error. * Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests. * As the `q` parameter is declared with `= None`, it is optional. * Without the `None` it would be required (as is the body in the case with `PUT`). * For `PUT` requests to `/items/{item_id}`, Read the body as JSON: * Check that it has a required attribute `name` that should be a `str`. * Check that it has a required attribute `price` that has to be a `float`. * Check that it has an optional attribute `is_offer`, that should be a `bool`, 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: ```Python return {"item_name": item.name, "item_id": item_id} ``` ...from: ```Python ... "item_name": item.name ... ``` ...to: ```Python ... "item_price": item.price ... ``` ...and see how your editor will auto-complete the attributes and know their types: ![editor support](https://fastapi.tiangolo.com/img/vscode-completion.png) For a more complete example including more features, see the Tutorial - User Guide. **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). * Many extra features (thanks to Starlette) as: * **WebSockets** * **GraphQL** * 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. ## 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 the `TestClient`. * aiofiles - Required if you want to use `FileResponse` or `StaticFiles`. * jinja2 - Required if you want to use the default template configuration. * python-multipart - Required if you want to support form "parsing", with `request.form()`. * itsdangerous - Required for `SessionMiddleware` support. * pyyaml - Required for Starlette's `SchemaGenerator` support (you probably don't need it with FastAPI). * graphene - Required for `GraphQLApp` support. * ujson - Required if you want to use `UJSONResponse`. Used by FastAPI / Starlette: * uvicorn - for the server that loads and serves your application. * orjson - Required if you want to use `ORJSONResponse`. You can install all of these with `pip install fastapi[all]`. ## License This project is licensed under the terms of the MIT license.