fast-api-non-annotated-dependency (FAST002)
Derived from the FastAPI linter.
Fix is sometimes available.
What it does
Identifies FastAPI routes with deprecated uses of Depends or similar.
Why is this bad?
The FastAPI documentation recommends the use of typing.Annotated
for defining route dependencies and parameters, rather than using Depends,
Query or similar as a default value for a parameter. Using this approach
everywhere helps ensure consistency and clarity in defining dependencies
and parameters.
Annotated was added to the typing module in Python 3.9; however,
the third-party typing_extensions package
provides a backport that can be used on older versions of Python.
Example
from fastapi import Depends, FastAPI
app = FastAPI()
async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
return {"q": q, "skip": skip, "limit": limit}
@app.get("/items/")
async def read_items(commons: dict = Depends(common_parameters)):
return commons
Use instead:
from typing import Annotated
from fastapi import Depends, FastAPI
app = FastAPI()
async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
return {"q": q, "skip": skip, "limit": limit}
@app.get("/items/")
async def read_items(commons: Annotated[dict, Depends(common_parameters)]):
return commons
Fix safety
This fix is always unsafe, as adding/removing/changing a function parameter's default value can change runtime behavior. Additionally, comments inside the deprecated uses might be removed.
Availability
Because this rule relies on the third-party typing_extensions module for Python versions
before 3.9, if the target version is < 3.9 and typing_extensions imports have been
disabled by the lint.typing-extensions linter option the diagnostic will not be emitted
and no fix will be offered.