* Validate that there is an `item_id` in the path for `GET` and `PUT` requests.
* Validate that the `item_id` is of type `int` for `GET` and `PUT` requests.
    * If it is not, the client will see a useful, clear error.
* Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests.
    * As the `q` parameter is declared with `= None`, it is optional.

* <a href="https://github.com/JoshData/python-email-validator" target="_blank"><code>email_validator</code></a> - per la validazione di email.

Usate da Starlette:

* <a href="http://docs.python-requests.org" target="_blank"><code>requests</code></a> - Richiesto se vuoi usare il `TestClient`.
* <a href="https://github.com/Tinche/aiofiles" target="_blank"><code>aiofiles</code></a> - Richiesto se vuoi usare `FileResponse` o `StaticFiles`.

* <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - Wymagany dla wsparcia `SessionMiddleware`.

* <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - Обязательно, для поддержки `SessionMiddleware`.

* <a href="https://jinja.palletsprojects.com" target="_blank"><code>jinja2</code></a> - 使用默认模板配置时安装。
* <a href="https://github.com/Kludex/python-multipart" target="_blank"><code>python-multipart</code></a> - 需要通过 `request.form()` 对表单进行<abbr title="将来自 HTTP 请求中的字符串转换为 Python 数据类型">「解析」</abbr>时安装。
* <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - 需要 `SessionMiddleware` 支持时安装。

-   <a href="https://github.com/Kludex/python-multipart" target="_blank"><code>python-multipart</code></a> - דרוש אם ברצונכם לתמוך ב <abbr title="המרת המחרוזת שמגיעה מבקשת HTTP למידע פייתון">"פרסור"</abbr> טפסים, באצמעות <code dir="ltr">request.form()</code>.
-   <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - דרוש אם ברצונכם להשתמש ב - `SessionMiddleware`.

* <a href="https://andrew-d.github.io/python-multipart/" target="_blank"><code>python-multipart</code></a> - erforderlich, wenn Sie Formulare mittels `request.form()` <abbr title="Konvertieren des Strings, der aus einer HTTP-Anfrage stammt, nach Python-Daten">„parsen“</abbr> möchten.

* <a href="https://github.com/Kludex/python-multipart" target="_blank"><code>python-multipart</code></a> - در صورتی که بخواهید با استفاده از `request.form()` از قابلیت <abbr title="تبدیل رشته متنی موجود در درخواست HTTP به انواع داده پایتون">"تجزیه (parse)"</abbr> فرم استفاده کنید.

* Kiểm tra xem có một `item_id` trong đường dẫn với các request `GET` và `PUT` không?
* Kiểm tra xem `item_id` có phải là kiểu `int` trong các request `GET` và `PUT` không?
    * Nếu không, client sẽ thấy một lỗi rõ ràng và hữu ích.
* Kiểm tra xem nếu có một tham số `q` trong query string (ví dụ như `http://127.0.0.1:8000/items/foo?q=somequery`) cho request `GET`.
    * Tham số `q` được định nghĩa `= None`, nó là tùy chọn.

And that function takes parameters in the same way that *path operation functions* do.

!!! tip
    You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.