flake8-fastapi

A flake8 plugin that helps you avoid simple FastAPI mistakes.

Installation

First, install the package:

pip install flake8-fastapi

Then, check if the plugin is installed using flake8:

$ flake8 --version
3.9.2 (flake8-fastapi: 0.2.0, flake8-pytest-style: 1.4.2, mccabe: 0.6.1, pycodestyle: 2.7.0, pyflakes: 2.3.1) CPython 3.8.11 on Linux

Rules

Route Decorator Error (CF001)

Developers that were used to flask can be persuaded or want to use the same pattern in FastAPI:

from fastapi import FastAPI

app = FastAPI()


@app.route("/", methods=["GET"])
def home():
    return "Hello world!"

But on FastAPI, we have a simpler way to define this (and is the most known way to create endpoints):

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def home():
    return "Hello world!"

Route Prefix Error (CF002)

On old FastAPI versions, we were able to add a prefix only on the include_router method:

from fastapi import APIRouter, FastAPI

router = APIRouter()


@router.get("/")
def home():
    ...


app = FastAPI()
app.include_router(router, prefix="/prefix")

Now, it's possible to add in the Router initialization:

from fastapi import APIRouter, FastAPI

router = APIRouter(prefix="/prefix")


@router.get("/")
def home():
    ...


app = FastAPI()
app.include_router(router)

CORSMiddleware Order (CF008)

There's a tricky issue about CORSMiddleware that people are usually unaware. Which is that this middleware should be the last one on the middleware stack. You can read more about it here.

Let's see an example of what doesn't work:

from fastapi import FastAPI

app = FastAPI()

app.add_middleware(
    CORSMiddleware,
    allow_origins=['*'],
    allow_credentials=True,
    allow_methods=['*'],
    allow_headers=['*']
)
app.add_middleware(GZipMiddleware)

As you see, the last middleware added is not CORSMiddleware, so it will not work as expected. On the other hand, if you change the order, it will:

from fastapi import FastAPI

app = FastAPI()

app.add_middleware(GZipMiddleware)
app.add_middleware(
    CORSMiddleware,
    allow_origins=['*'],
    allow_credentials=True,
    allow_methods=['*'],
    allow_headers=['*']
)

License

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