},
)
async def b():
    return "b"


@router.get(
    "/c",
    responses={
        "400": {"description": "Error with str"},
        "5xx": {"description": "Error with range, lower"},
        "default": {"description": "A default response"},
    },
)
async def c():
    return "c"


@router.get(
    "/d",
    responses={
        "400": {"description": "Error with str"},

By the last <a href="https://www.jetbrains.com/research/python-developers-survey-2018/#development-tools" class="external-link" target="_blank">Python Developer Survey</a>, that covers about 80% of the users.

    class ModelC(ModelB):
        password: str

    class ModelA(BaseModel):
        name: str
        description: Optional[str] = None
        foo: ModelB

        @field_validator("name")
        def lower_username(cls, name: str, info: ValidationInfo):
            if not name.endswith("A"):
                raise ValueError("name must end in A")
            return name

    async def get_model_c() -> ModelC:

- login: Smlep
  count: 11
  avatarUrl: https://avatars.githubusercontent.com/u/16785985?v=4
  url: https://github.com/Smlep
- login: hard-coders
  count: 10
  avatarUrl: https://avatars.githubusercontent.com/u/9651103?u=95db33927bbff1ed1c07efddeb97ac2ff33068ed&v=4
  url: https://github.com/hard-coders
- login: alejsdev
  count: 10
  avatarUrl: https://avatars.githubusercontent.com/u/90076947?u=1ee3a9fbef27abc9448ef5951350f99c7d76f7af&v=4

```

### Declare a `list` with a type parameter

To declare types that have type parameters (internal types), like `list`, `dict`, `tuple`:

* If you are in a Python version lower than 3.9, import their equivalent version from the `typing` module
* Pass the internal type(s) as "type parameters" using square brackets: `[` and `]`

In Python 3.9 it would be:

```Python
my_list: list[str]
```

There you could buy me a coffee ☕️ to say thanks. 😄

And you can also become a Silver or Gold sponsor for FastAPI. 🏅🎉

## Sponsor the tools that power FastAPI

As you have seen in the documentation, FastAPI stands on the shoulders of giants, Starlette and Pydantic.

You can also sponsor:

        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params_str_validations/tutorial006c.py!}
    ```

!!! tip

> Modern versions of Python have support for **"asynchronous code"** using something called **"coroutines"**, with **`async` and `await`** syntax.

That should make more sense now. ✨

All that is what powers FastAPI (through Starlette) and what makes it have such an impressive performance.

## Very Technical Details

!!! warning
    You can probably skip this.

!!! tip
    This will just make Peewee behave correctly when used with FastAPI. Not randomly opening or closing connections that are being used, creating errors, etc.

    But it doesn't give Peewee async super-powers. You should still use normal `def` functions and not `async def`.

### Use the custom `PeeweeConnectionState` class

    username: str


class ModelC(ModelB):
    password: str


class ModelA(BaseModel):
    name: str
    description: Optional[str] = None
    model_b: ModelB

    @validator("name")
    def lower_username(cls, name: str, values):
        if not name.endswith("A"):
            raise ValueError("name must end in A")
        return name


async def get_model_c() -> ModelC: