When you use FastAPI, you might be tempted to create sync (def) dependencies, on which you actually don't perform thread blocking operations. The thing is that FastAPI will always run your sync dependencies in a thread pool, which is not always necessary.

The goal of this package is to make explicit if you want to run a dependency in a thread pool.

Installation

The package is available on PyPI:

pip install fastapi-dependency

Usage

This package is really small and contains simple functions:

Depends

Signature: Depends(dependency: Callable[..., Any] | None = None, *, use_cache: bool = True, use_thread_pool: bool | None = None)

This function is a drop-in replacement for fastapi.Depends and it has the same signature. The only difference is that it has an extra parameter: use_thread_pool.

If you want to run a dependency in a thread pool, you can set use_thread_pool to True.

from fastapi import FastAPI
from fastapi_dependency import Depends

app = FastAPI()


def dependency():
    return "Hello World!"

@app.get("/")
def index(message: str = Depends(dependency, use_thread_pool=True)):
    return {"message": message}

If you don't set use_thread_pool on sync dependencies, it will raise a RuntimeError.

ThreadDepends

Signature: ThreadDepends(dependency: Callable[..., Any] | None = None, *, use_cache: bool = True)

This function is a drop-in replacement for fastapi.Depends and it has the same signature. The only difference is that it will always run the dependency in a thread pool.

from fastapi import FastAPI
from fastapi_dependency import ThreadDepends

app = FastAPI()


def dependency():
    return "Hello World!"

@app.get("/")
def index(message: str = ThreadDepends(dependency)):
    return {"message": message}

ThreadlessDepends

Signature: ThreadlessDepends(dependency: Callable[..., Any] | None = None, *, use_cache: bool = True)

This function is a drop-in replacement for fastapi.Depends and it has the same signature. The only difference is that it will never run the dependency in a thread pool.

from fastapi import FastAPI
from fastapi_dependency import ThreadlessDepends

app = FastAPI()


def dependency():
    return "Hello World!"

@app.get("/")
def index(message: str = ThreadlessDepends(dependency)):
    return {"message": message}

Security

The analogous functions for fastapi.Security are:

• Security
• ThreadSecurity
• ThreadlessSecurity

License

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