It will be called by **FastAPI** whenever it receives a request to the URL "`/`" using a `GET` operation.

In this case, it is an `async` function.

---

You could also define it as a normal function instead of `async def`:

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial003.py!}
```

!!! note

| `license_info` | `dict` | Die Lizenzinformationen für die verfügbar gemachte API. Kann mehrere...

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                    "required": ["file"],
                    "type": "object",
                    "properties": {
                        "file": {"title": "File", "type": "string", "format": "binary"}
                    },
                },
                "Body_create_file_files__post": {
                    "title": "Body_create_file_files__post",
                    "required": ["file"],

                    "required": ["file"],
                    "type": "object",
                    "properties": {
                        "file": {"title": "File", "type": "string", "format": "binary"}
                    },
                },
                "Body_create_file_files__post": {
                    "title": "Body_create_file_files__post",
                    "required": ["file"],

    * This allows adding extra code after a dependency is done. It can be used, for example, to close database connections.
    * Dependencies with `yield` can be normal or `async`, **FastAPI** will run normal dependencies in a threadpool.
    * They can be combined with normal dependencies.
    * It's possible to have arbitrary trees/levels of dependencies with `yield` and exit steps are handled in the correct order automatically.

    # Ref: JSON Schema Validation 2020-12: https://json-schema.org/draft/2020-12/json-schema-validation.html#name-vocabularies-for-semantic-c
    # Vocabularies for Semantic Content With "format"
    format: Optional[str] = None
    # Ref: JSON Schema Validation 2020-12: https://json-schema.org/draft/2020-12/json-schema-validation.html#name-a-vocabulary-for-the-conten
    # A Vocabulary for the Contents of String-Encoded Data

4️⃣. `Author` 🎻 ⚙️ `response_model` 🔢.

5️⃣. 👆 💪 ⚙️ 🎏 🐩 🆎 ✍ ⏮️ 🎻 📨 💪.

    👉 💼, ⚫️ 📇 `Item` 🎻.

6️⃣. 📥 👥 🛬 📖 👈 🔌 `items` ❔ 📇 🎻.

    FastAPI 🎯 <abbr title="converting the data to a format that can be transmitted">✍</abbr> 💽 🎻.

7️⃣. 📥 `response_model` ⚙️ 🆎 ✍ 📇 `Author` 🎻.

    🔄, 👆 💪 🌀 `dataclasses` ⏮️ 🐩 🆎 ✍.

8️⃣. 👀 👈 👉 *➡ 🛠️ 🔢* ⚙️ 🥔 `def` ↩️ `async def`.

            field_schema.update({"type": "string", "format": "binary"})

    @classmethod
    def __get_pydantic_json_schema__(
        cls, core_schema: CoreSchema, handler: GetJsonSchemaHandler
    ) -> JsonSchemaValue:
        return {"type": "string", "format": "binary"}

    @classmethod
    def __get_pydantic_core_schema__(

                    "properties": {
                        "file": {"title": "File", "type": "string", "format": "binary"},
                        "fileb": {
                            "title": "Fileb",
                            "type": "string",
                            "format": "binary",
                        },
                        "token": {"title": "Token", "type": "string"},
                    },