FastAPI framework, high performance, easy to learn, fast to code, ready for production
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:
* estimation based on tests on an internal development team, building production applications.
"[...] 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."
"We adopted the FastAPI library to spawn a REST server that can be queried to obtain predictions. [for Ludwig]"
"Netflix is pleased to announce the open-source release of our crisis management orchestration framework: Dispatch! [built with FastAPI]"
"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."
"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."
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. ⌨️ 🚀
FastAPI stands on the shoulders of giants:
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.
main.py with: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}
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 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.
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.
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:
/ and /items/{item_id}.GET operations (also known as HTTP methods)./items/{item_id} has a path parameter item_id that should be an int./items/{item_id} has an optional str query parameter q.Now go to http://127.0.0.1:8000/docs.
You will see the automatic interactive API documentation (provided by Swagger UI):
And now, go to http://127.0.0.1:8000/redoc.
You will see the alternative automatic documentation (provided by ReDoc):
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.
Now go to http://127.0.0.1:8000/docs.
And now, go to http://127.0.0.1:8000/redoc.
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:
str, int, float, bool, list, etc).datetime objects.UUID objects.Coming back to the previous code example, FastAPI will:
item_id in the path for GET and PUT requests.item_id is of type int for GET and PUT requests.
q (as in http://127.0.0.1:8000/items/foo?q=somequery) for GET requests.
q parameter is declared with = None, it is optional.None it would be required (as is the body in the case with PUT).PUT requests to /items/{item_id}, read the body as JSON:
name that should be a str.price that has to be a float.is_offer, that should be a bool, if present.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 the Tutorial - User Guide.
Spoiler alert: the tutorial - user guide includes:
maximum_length or regex.pytestIndependent 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.
FastAPI depends on Pydantic and Starlette.
standard DependenciesWhen 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.standard DependenciesIf you don't want to include the standard optional dependencies, you can install with pip install fastapi instead of pip install "fastapi[standard]".
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.This project is licensed under the terms of the MIT license.
FAQs
FastAPI framework, high performance, easy to learn, fast to code, ready for production
We found that fastapi demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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