### 🔁 1️⃣: 🗄 `FastAPI`

```Python hl_lines="1"
{!../../../docs_src/first_steps/tutorial001.py!}
```

`FastAPI` 🐍 🎓 👈 🚚 🌐 🛠️ 👆 🛠️.

!!! note "📡 ℹ"
    `FastAPI` 🎓 👈 😖 🔗 ⚪️➡️ `Starlette`.

    👆 💪 ⚙️ 🌐 <a href="https://www.starlette.io/" class="external-link" target="_blank">💃</a> 🛠️ ⏮️ `FastAPI` 💁‍♂️.

### 🔁 2️⃣: ✍ `FastAPI` "👐"

```Python hl_lines="3"

```Python hl_lines="4  14  16-22"
{!../../../docs_src/async_sql_databases/tutorial001.py!}
```

!!! tip
    Notice that all this code is pure SQLAlchemy Core.

    `databases` is not doing anything here yet.

## Import and set up `databases`

* Import `databases`.
* Create a `DATABASE_URL`.
* Create a `database` object.

```Python hl_lines="3  9  12"

	// color characters, the result is incorrect.
	line1Length := len(fmt.Sprintf(msgLine1Fmt, newerThan))
	line2Length := len(fmt.Sprintf(msgLine2Fmt, updateString))

	// Populate lines with color coding.
	line1InColor := fmt.Sprintf(msgLine1Fmt, color.YellowBold(newerThan))
	line2InColor := fmt.Sprintf(msgLine2Fmt, color.CyanBold(updateString))

	// calculate the rectangular box size.

✍ 🗃 👆 🔖 & 🚶‍♀️ ⚫️ `openapi_tags` 🔢:

```Python hl_lines="3-16  18"
{!../../../docs_src/metadata/tutorial004.py!}
```

👀 👈 👆 💪 ⚙️ ✍ 🔘 📛, 🖼 "💳" 🔜 🎦 🦁 (**💳**) & "🎀" 🔜 🎦 ❕ (_🎀_).

!!! tip
    👆 🚫 ✔️ 🚮 🗃 🌐 🔖 👈 👆 ⚙️.

### ⚙️ 👆 🔖

⚙️ `tags` 🔢 ⏮️ 👆 *➡ 🛠️* (& `APIRouter`Ⓜ) 🛠️ 👫 🎏 🔖:

```Python hl_lines="21  26"
{!../../../docs_src/metadata/tutorial004.py!}
```

アプリ開発中に本体のログを取ってデバッグしたり、ユーザーに返したりなどに使用することができます。

```Python hl_lines="14"
{!../../../docs_src/handling_errors/tutorial005.py!}
```

ここで、以下のような無効な項目を送信してみてください:

```JSON
{
  "title": "towel",
  "size": "XL"
}
```

受信したボディを含むデータが無効であることを示すレスポンスが表示されます:

```JSON hl_lines="12 13 14 15"
{
  "detail": [
    {
      "loc": [
        "body",

All we need to do is handle the request inside a `try`/`except` block:

```Python hl_lines="13  15"
{!../../../docs_src/custom_request_and_route/tutorial002.py!}
```

If an exception occurs, the`Request` instance will still be in scope, so we can read and make use of the request body when handling the error:

```Python hl_lines="16-18"
{!../../../docs_src/custom_request_and_route/tutorial002.py!}
```

=== "🐍 3️⃣.6️⃣ & 🔛"

    ```Python hl_lines="3  6-8  11-12  23-24  27-28"
    {!> ../../../docs_src/sql_databases/sql_app/schemas.py!}
    ```

=== "🐍 3️⃣.9️⃣ & 🔛"

    ```Python hl_lines="3  6-8  11-12  23-24  27-28"
    {!> ../../../docs_src/sql_databases/sql_app_py39/schemas.py!}
    ```

=== "🐍 3️⃣.1️⃣0️⃣ & 🔛"

    ```Python hl_lines="1  4-6  9-10  21-22  25-26"

```Python hl_lines="1  3" title="app/routers/users.py"
{!../../../docs_src/bigger_applications/app/routers/users.py!}
```

### *Path operations* with `APIRouter`

And then you use it to declare your *path operations*.

Use it the same way you would use the `FastAPI` class:

```Python hl_lines="6  11  16" title="app/routers/users.py"

↩️ *➡ 🛠️* 🔬 ✔, 👆 💪 ⚒ 💭 👈 ➡ `/users/me` 📣 ⏭ 1️⃣ `/users/{user_id}`:

```Python hl_lines="6  11"
{!../../../docs_src/path_params/tutorial003.py!}
```

⏪, ➡ `/users/{user_id}` 🔜 🏏 `/users/me`, "💭" 👈 ⚫️ 📨 🔢 `user_id` ⏮️ 💲 `"me"`.

➡, 👆 🚫🔜 ↔ ➡ 🛠️:

```Python hl_lines="6  11"
{!../../../docs_src/path_params/tutorial003b.py!}
```

🥇 🕐 🔜 🕧 ⚙️ ↩️ ➡ 🏏 🥇.

## 🔁 💲

그리고 특정 순서로 선언할 필요가 없습니다.

매개변수들은 이름으로 감지됩니다:

```Python hl_lines="8  10"
{!../../../docs_src/query_params/tutorial004.py!}
```

## 필수 쿼리 매개변수

경로가 아닌 매개변수에 대한 기본값을 선언할 때(지금은 쿼리 매개변수만 보았습니다), 해당 매개변수는 필수적(Required)이지 않았습니다.

특정값을 추가하지 않고 선택적으로 만들기 위해선 기본값을 `None`으로 설정하면 됩니다.

그러나 쿼리 매개변수를 필수로 만들려면 단순히 기본값을 선언하지 않으면 됩니다:

```Python hl_lines="6-7"
{!../../../docs_src/query_params/tutorial005.py!}
```