{!../../docs_src/query_params/tutorial002.py!}
```

이 경우 함수 매개변수 `q`는 선택적이며 기본값으로 `None` 값이 됩니다.

/// check | "확인"

**FastAPI**는 `item_id`가 경로 매개변수이고 `q`는 경로 매개변수가 아닌 쿼리 매개변수라는 것을 알 정도로 충분히 똑똑합니다.

///

/// note | "참고"

FastAPI는 `q`가 `= None`이므로 선택적이라는 것을 인지합니다.

`Union[str, None]`에 있는 `Union`은 FastAPI(FastAPI는 `str` 부분만 사용합니다)가 사용하는게 아니지만, `Union[str, None]`은 편집기에게 코드에서 오류를 찾아낼 수 있게 도와줍니다.

///

## 쿼리 매개변수 형변환

import pytest
from fastapi.testclient import TestClient

from tests.utils import needs_py39, needs_pydanticv2


@pytest.fixture(name="client")
def get_client():
    from docs_src.request_form_models.tutorial002_an_py39 import app

    client = TestClient(app)
    return client


@needs_pydanticv2
@needs_py39
def test_post_body_form(client: TestClient):

import pytest
from dirty_equals import IsDict
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(name="client")
def get_client():
    from docs_src.body_fields.tutorial001_an_py310 import app

    client = TestClient(app)
    return client


@needs_py310
def test_items_5(client: TestClient):
    response = client.put("/items/5", json={"item": {"name": "Foo", "price": 3.0}})

from dirty_equals import IsDict
from fastapi.testclient import TestClient

from docs_src.request_files.tutorial001_02_an import app

client = TestClient(app)


def test_post_form_no_body():
    response = client.post("/files/")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "No file sent"}


def test_post_uploadfile_no_body():
    response = client.post("/uploadfile/")

* 🚥 🔢 📣 **➡**, ⚫️ 🔜 ⚙️ ➡ 🔢.
* 🚥 🔢 **⭐ 🆎** (💖 `int`, `float`, `str`, `bool`, ♒️) ⚫️ 🔜 🔬 **🔢** 🔢.
* 🚥 🔢 📣 🆎 **Pydantic 🏷**, ⚫️ 🔜 🔬 📨 **💪**.

/// note

FastAPI 🔜 💭 👈 💲 `q` 🚫 ✔ ↩️ 🔢 💲 `= None`.

 `Union` `Union[str, None]` 🚫 ⚙️ FastAPI, ✋️ 🔜 ✔ 👆 👨‍🎨 🤝 👆 👍 🐕‍🦺 & 🔍 ❌.

///

## 🍵 Pydantic

# Sobre

{!../../docs_src/dependencies/tutorial011.py!}
```

👉 💼, 👉 `__call__` ⚫️❔ **FastAPI** 🔜 ⚙️ ✅ 🌖 🔢 & 🎧-🔗, & 👉 ⚫️❔ 🔜 🤙 🚶‍♀️ 💲 🔢 👆 *➡ 🛠️ 🔢* ⏪.

## 🔗 👐

& 🔜, 👥 💪 ⚙️ `__init__` 📣 🔢 👐 👈 👥 💪 ⚙️ "🔗" 🔗:

```Python hl_lines="7"
{!../../docs_src/dependencies/tutorial011.py!}
```

👉 💼, **FastAPI** 🏆 🚫 ⏱ 👆 ⚖️ 💅 🔃 `__init__`, 👥 🔜 ⚙️ ⚫️ 🔗 👆 📟.

## ✍ 👐

👥 💪 ✍ 👐 👉 🎓 ⏮️:

from typing import List, Union

from fastapi import Depends, FastAPI, HTTPException, Query
from sqlmodel import Field, Session, SQLModel, create_engine, select


class HeroBase(SQLModel):
    name: str = Field(index=True)
    age: Union[int, None] = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: Union[int, None] = Field(default=None, primary_key=True)
    secret_name: str


class HeroPublic(HeroBase):

from typing import Annotated

from fastapi import Depends, FastAPI, HTTPException, Query
from sqlmodel import Field, Session, SQLModel, create_engine, select


class HeroBase(SQLModel):
    name: str = Field(index=True)
    age: int | None = Field(default=None, index=True)


class Hero(HeroBase, table=True):
    id: int | None = Field(default=None, primary_key=True)
    secret_name: str


class HeroPublic(HeroBase):
    id: int

```Python hl_lines="2  6"
{!../../docs_src/static_files/tutorial001.py!}
```

/// note | "技术细节"

你也可以用 `from starlette.staticfiles import StaticFiles`。

**FastAPI** 提供了和 `starlette.staticfiles` 相同的 `fastapi.staticfiles` ，只是为了方便你，开发者。但它确实来自Starlette。

///

### 什么是"挂载"(Mounting)

"挂载" 表示在特定路径添加一个完全"独立的"应用，然后负责处理所有子路径。

这与使用`APIRouter`不同，因为安装的应用程序是完全独立的。OpenAPI和来自你主应用的文档不会包含已挂载应用的任何东西等等。