FastAPI Depends() DI flagged by Flake8 Bugbear Linting

See original GitHub issue

Flake8 Bugbear is a linting tool that points out potential bugs and design problems in applications. While doing linting on my FastAPI project, bugbear calls out:

B008 Do not perform function calls in argument defaults. The call is performed only once at function definition time. All calls to your function will reuse the result of that definition-time function call. If this is intended, assign the function call to a module-level variable and use that variable as a default value.

… for any Depends() usage in a method signature, such as:

async def login(response: Response,
                request: Request,
                form_data:
                OAuth2PasswordRequestForm = Depends())

I’m not flagging this as a bug, but just wanted to raise it to get your design opinion, as apparently someone out there thinks the Depends() pattern is not very pythonic.

Issue Analytics

State:
Created 3 years ago
Reactions:1
Comments:5 (2 by maintainers)

Top GitHub Comments

7reactions

adam-olemacommented, Oct 30, 2021

For those who want to keep bugbear but not disable the checks entirely for every line that uses Depends, the following small plugin will amend bugbear’s rules to recognize Depends as immutable, Unfortunately, BugBear does not provide a simpler configuration process.



from typing import Any

import bugbear

class Extension(object):
    name = "bugbear_fastapi_depends"
    version = 1

    def __init__(self, noqa: Any) -> None:
        pass

bugbear.B008.immutable_calls.update([
    "fastapi.Depends",
    "fastapi.params.Depends",
    "Depends",
])

For local usage, from setup.cfg, you can do:

[flake8:local-plugins]
extension =
     BB8F = module.of.my.extension:Extension

6reactions

ShaneNolancommented, May 10, 2022

Anyone using a setup.cfg flake8 configuration can use the extend-immutable-calls keyword to allow Depends().

[flake8]
...
extend-immutable-calls = fastapi.Depends, fastapi.params.Depends

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