from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(*, item_id: int = Path(title="The ID of the item to get"), q: str):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

from datetime import datetime
from typing import Union

from fastapi import FastAPI
from fastapi.encoders import jsonable_encoder
from fastapi.responses import JSONResponse
from pydantic import BaseModel


class Item(BaseModel):
    title: str
    timestamp: datetime
    description: Union[str, None] = None


app = FastAPI()


@app.put("/items/{id}")
def update_item(id: str, item: Item):

You can use the `TestClient` class to test FastAPI applications without creating an actual HTTP and socket connection, just communicating directly with the FastAPI code.

Read more about it in the [FastAPI docs for Testing](https://fastapi.tiangolo.com/tutorial/testing/).

You can import it directly from `fastapi.testclient`:

```python
from fastapi.testclient import TestClient
```

from fastapi import FastAPI, Query

app = FastAPI()


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

from typing import Annotated, Union

from fastapi import FastAPI, Form
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class UserForm(BaseModel):
    name: str
    email: str


class CompanyForm(BaseModel):
    company_name: str
    industry: str


@app.post("/form-union/")
def post_union_form(data: Annotated[Union[UserForm, CompanyForm], Form()]):

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 typing import Annotated

from fastapi import Cookie, FastAPI
from pydantic import BaseModel

app = FastAPI()


class Cookies(BaseModel):
    session_id: str
    fatebook_tracker: str | None = None
    googall_tracker: str | None = None


@app.get("/items/")
async def read_items(cookies: Annotated[Cookies, Cookie()]):

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


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

...
```

#### OpenAPI 的用途

驱动 FastAPI 内置的 2 个交互式文档系统的正是 OpenAPI 模式。

并且还有数十种替代方案，它们全部都基于 OpenAPI。你可以轻松地将这些替代方案中的任何一种添加到使用 **FastAPI** 构建的应用程序中。

你还可以使用它自动生成与你的 API 进行通信的客户端代码。例如 web 前端，移动端或物联网嵌入程序。

## 分步概括

### 步骤 1：导入 `FastAPI`

{* ../../docs_src/first_steps/tutorial001.py hl[1] *}

`FastAPI` 是一个为你的 API 提供了所有功能的 Python 类。

/// note | 技术细节

## Utilize o comando `fastapi run` { #use-the-fastapi-run-command }

Em resumo, utilize o comando `fastapi run` para inicializar sua aplicação FastAPI:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> run <u style="text-decoration-style:solid">main.py</u>

  <span style="background-color:#009485"><font color="#D3D7CF"> FastAPI </font></span>  Starting production server 🚀