Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.

Es könnten nur eine oder zwei Codezeilen sein, wie zum Beispiel:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

此处唯一比较新的内容是*路径操作装饰器*中的 `callbacks=invoices_callback_router.routes` 参数，下文介绍。

## 存档回调

实际的回调代码高度依赖于您自己的 API 应用。

并且可能每个应用都各不相同。

回调代码可能只有一两行，比如：

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
requests.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

## 🔬 ⏲

☑ ⏲ 📟 🔜 🪀 🙇 🔛 👆 👍 🛠️ 📱.

& ⚫️ 🔜 🎲 🪀 📚 ⚪️➡️ 1️⃣ 📱 ⏭.

⚫️ 💪 1️⃣ ⚖️ 2️⃣ ⏸ 📟, 💖:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

✋️ 🎲 🏆 ⚠ 🍕 ⏲ ⚒ 💭 👈 👆 🛠️ 👩‍💻 (🔢 👩‍💻) 🛠️ *🔢 🛠️* ☑, 🛄 💽 👈 *👆 🛠️* 🔜 📨 📨 💪 ⏲, ♒️.

  - type: dropdown
    id: author-go-experience
    attributes:
      label: "Go Programming Experience"
      description: "Would you consider yourself a novice, intermediate, or experienced Go programmer?"
      options:
        - "Novice"
        - "Intermediate"
        - "Experienced"
      default: 1

  - type: input
    id: author-other-languages-experience
    attributes:

Et c'est le cas pour la plupart des applications web.

Vous aurez de nombreux, nombreux utilisateurs, mais votre serveur attendra 🕙 que leur connexion peu performante envoie des requêtes.

Puis vous attendrez 🕙 de nouveau que leurs réponses reviennent.

Cette "attente" 🕙 se mesure en microsecondes, mais tout de même, en cumulé cela fait beaucoup d'attente.