In the end, the ultimate objective is to be able to **serve your API clients** in a way that is **secure**, to **avoid disruptions**, and to use the **compute resources** (for example remote servers/virtual machines) as efficiently as possible. 🚀

    ```

=== "Python 3.8+"

    ```Python
    {!> ../../../docs_src/security/tutorial001_an.py!}
    ```

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python
    {!> ../../../docs_src/security/tutorial001.py!}
    ```


## Run it

!!! info

=== "Python 3.8+"

    ```Python hl_lines="16"
    {!> ../../../docs_src/dependencies/tutorial012_an.py!}
    ```

=== "Python 3.8 non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="15"
    {!> ../../../docs_src/dependencies/tutorial012.py!}
    ```

    assert e.value.code == status.WS_1008_POLICY_VIOLATION
    # and no error is leaked
    assert caught == []


def test_depend_err_middleware():
    """
    Verify that it is possible to write custom WebSocket middleware to catch errors
    """

    @websocket_middleware
    async def errorhandler(websocket: WebSocket, call_next):
        try:
            return await call_next()

In Python 3.6 and above (including Python 3.10) you can use the `Union` type from `typing` and put inside the square brackets the possible types to accept.

In Python 3.10 there's also a **new syntax** where you can put the possible types separated by a <abbr title='also called "bitwise or operator", but that meaning is not relevant here'>vertical bar (`|`)</abbr>.

=== "Python 3.10+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/header_params/tutorial003_an.py!}
    ```

=== "Python 3.10+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="7"
    {!> ../../../docs_src/header_params/tutorial003_py310.py!}
    ```

=== "Python 3.9+ non-Annotated"

    !!! tip
        尽可能选择使用 `Annotated` 的版本。

    {!> ../../../docs_src/bigger_applications/app_an/dependencies.py!}
    ```

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="1  4-6" title="app/dependencies.py"
    {!> ../../../docs_src/bigger_applications/app/dependencies.py!}
    ```

!!! tip
    We are using an invented header to simplify this example.

    * This includes support for ASGI 3 (the latest version of the standard).
    * It's now possible to use [Starlette's `StreamingResponse`](https://www.starlette.io/responses/#streamingresponse) with iterators, like [file-like](https://docs.python.org/3/glossary.html#term-file-like-object) objects (as those returned by `open()`).
    * It's now possible to use the low level utility `iterate_in_threadpool` from `starlette.concurrency` (for advanced scenarios).

    ```

=== "Python 3.10 non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="6-7"
    {!> ../../../docs_src/dependencies/tutorial005_py310.py!}
    ```

=== "Python 3.8 non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="8-9"
    {!> ../../../docs_src/dependencies/tutorial005.py!}
    ```

=== "Python 3.10+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="7"
    {!> ../../../docs_src/query_params_str_validations/tutorial003_py310.py!}
    ```

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="10"