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https://github.com/fastapi/fastapi

FastAPI framework, high performance, easy to learn, fast to code, ready for production
https://github.com/fastapi/fastapi

api async asyncio fastapi framework json json-schema openapi openapi3 pydantic python python-types python3 redoc rest starlette swagger swagger-ui uvicorn web

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

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FastAPI



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




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---

**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 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
















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)

---

"_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:

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

## Installation

Create and activate a virtual environment and then install FastAPI:

```console
$ pip install "fastapi[standard]"

---> 100%
```

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

## Example

### Create it

* Create a file `main.py` with:

```Python
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`:

```Python hl_lines="9 14"
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:

```console
$ 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:

```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 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.

* 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**.

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).
* **GraphQL** integration with Strawberry and other libraries.
* Many extra features (thanks to Starlette) as:
* **WebSockets**
* extremely easy tests based on HTTPX 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.

## 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:

* email-validator - for email validation.

Used by Starlette:

* httpx - Required if you want to use the `TestClient`.
* jinja2 - Required if you want to use the default template configuration.
* python-multipart - Required if you want to support form "parsing", with `request.form()`.

Used by FastAPI / Starlette:

* uvicorn - for the server that loads and serves your application. This includes `uvicorn[standard]`, which includes some dependencies (e.g. `uvloop`) needed for high performance serving.
* `fastapi-cli` - to provide the `fastapi` command.

### 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:

* 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 use `ORJSONResponse`.
* ujson - Required if you want to use `UJSONResponse`.

## License

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