min_length: Annotated[
        Optional[int],
        Doc(
            """
            Minimum length for strings.
            """
        ),
    ] = None,
    max_length: Annotated[
        Optional[int],
        Doc(
            """
            Maximum length for strings.
            """
        ),
    ] = None,
    pattern: Annotated[
        Optional[str],
        Doc(

    ```

## Set-Typen

Aber dann denken wir darüber nach und stellen fest, dass sich die Tags nicht wiederholen sollen, es sollen eindeutige Strings sein.

Python hat einen Datentyp speziell für Mengen eindeutiger Dinge: das <abbr title="Menge">`set`</abbr>.

Deklarieren wir also `tags` als Set von Strings.

=== "Python 3.10+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/body_nested_models/tutorial003_py310.py!}
    ```

    - **name**: each item must have a name
    - **description**: a long description
    - **price**: required
    - **tax**: if the item doesn't have tax, you can omit this
    - **tags**: a set of unique tag strings for this item
    """

```JSON
{"item_id":3}
```

!!! check
    Notice that the value your function received (and returned) is `3`, as a Python `int`, not a string `"3"`.

    So, with that type declaration, **FastAPI** gives you automatic request <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>.

## Data validation

                            "items": {
                                "anyOf": [{"type": "string"}, {"type": "integer"}]
                            },
                        },
                        "msg": {"title": "Message", "type": "string"},
                        "type": {"title": "Error Type", "type": "string"},
                    },
                },
            }
        },

    - **name**: each item must have a name
    - **description**: a long description
    - **price**: required
    - **tax**: if the item doesn't have tax, you can omit this
    - **tags**: a set of unique tag strings for this item
    """

    - **name**: each item must have a name
    - **description**: a long description
    - **price**: required
    - **tax**: if the item doesn't have tax, you can omit this
    - **tags**: a set of unique tag strings for this item
    \f
    :param item: User input.
    """

👆 💪 🛠️ ⚫️ 🙆 🎏 ☁ 💽 💖:

* **✳**
* **👸**
* **✳**
* **🇸🇲**
* **✳**, ♒️.

!!! tip

{!../../../docs_src/nosql_databases/tutorial001.py!}
```

### f-strings

If you are not familiar with the `f"userprofile::{username}"`, it is a Python "<a href="https://docs.python.org/3/glossary.html#term-f-string" class="external-link" target="_blank">f-string</a>".

Any variable that is put inside of `{}` in an f-string will be expanded / injected in the string.

### `dict` unpacking

# Pfad-Parameter

Sie können Pfad-„Parameter“ oder -„Variablen“ mit der gleichen Syntax deklarieren, welche in Python-<abbr title="Format-String – Formatierter String: Der String enthält Variablen, die mit geschweiften Klammern umschlossen sind. Solche Stellen werden durch den Wert der Variable ersetzt">Format-Strings</abbr> verwendet wird:

```Python hl_lines="6-7"
{!../../../docs_src/path_params/tutorial001.py!}
```