/// warning | 注意

你大概率不需要了解这些技术细节，可以跳过这一章节继续阅读后续的内容。

如果你使用的FastAPI的版本早于0.106.0，并且在使用后台任务中使用了包含 `yield` 的依赖项中的资源，那么这些细节会对你有一些用处。

///

### 包含 `yield` 和 `except` 的依赖项的技术细节

在FastAPI 0.110.0版本之前，如果使用了一个包含 `yield` 的依赖项，你在依赖项中使用 `except` 捕获了一个异常，但是你没有再次抛出该异常，这个异常会被自动抛出/转发到异常处理器或者内部服务错误处理器。

### 后台任务和使用 `yield` 的依赖项的技术细节

在FastAPI 0.106.0版本之前，在 `yield` 后面抛出异常是不可行的，因为 `yield` 之后的退出代码是在响应被发送之后再执行，这个时候异常处理器已经执行过了。

from fastapi import FastAPI
from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):
    item_dict = item.dict()
    if item.tax:
        price_with_tax = item.price + item.tax
        item_dict.update({"price_with_tax": price_with_tax})

from typing import Union

from fastapi import FastAPI, Path, Query

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(
    item_id: int = Path(title="The ID of the item to get"),
    q: Union[str, None] = Query(default=None, alias="item-query"),
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[str | None, Query(min_length=3, max_length=50)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

from functools import lru_cache

from fastapi import Depends, FastAPI

from .config import Settings

app = FastAPI()


@lru_cache
def get_settings():
    return Settings()


@app.get("/info")
async def info(settings: Settings = Depends(get_settings)):
    return {
        "app_name": settings.app_name,
        "admin_email": settings.admin_email,
        "items_per_user": settings.items_per_user,

from fastapi import FastAPI
from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None


app = FastAPI()


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):

from dataclasses import dataclass
from typing import Union

from fastapi import FastAPI


@dataclass
class Item:
    name: str
    price: float
    description: Union[str, None] = None
    tax: Union[float, None] = None


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):

O que inspirou o **FastAPI**, como ele se compara às alternativas e o que FastAPI aprendeu delas.

## Introdução

**FastAPI** não poderia existir se não fosse pelos trabalhos anteriores de outras pessoas.

Houveram tantas ferramentas criadas que ajudaram a inspirar sua criação.