And as the `Response` can be used frequently to set headers and cookies, **FastAPI** also provides it at `fastapi.Response`.

                automatically cancel the request and send the client an error.

                If `auto_error` is set to `False`, when the query parameter is not
                available, instead of erroring out, the dependency result will be
                `None`.

                This is useful when you want to have optional authentication.

# Deployment

Deploying a **FastAPI** application is relatively easy.

## What Does Deployment Mean

To **deploy** an application means to perform the necessary steps to make it **available to the users**.

For a **web API**, it normally involves putting it in a **remote machine**, with a **server program** that provides good performance, stability, etc, so that your **users** can **access** the application efficiently and without interruptions or problems.

在新的 Terminal 里，用以下命令确认 CLI 是否正确安装：

<div class="termy">

```console
$ deta --help

Deta command line interface for managing deta micros.
Complete documentation available at https://docs.deta.sh

Usage:
  deta [flags]
  deta [command]

Available Commands:
  auth        Change auth settings for a deta micro

...
```

</div>

!!! tip "提示"

    **FastAPI** provides the same `starlette.responses` as `fastapi.responses` just as a convenience for you, the developer. But most of the available responses come directly from Starlette. The same with `Request`.

## Override the default exception handlers

**FastAPI** has some default exception handlers.

    You could also use `from starlette.templating import Jinja2Templates`.

    **FastAPI** provides the same `starlette.templating` as `fastapi.templating` just as a convenience for you, the developer. But most of the available responses come directly from Starlette. The same with `Request` and `StaticFiles`.

## Writing templates

Then you can write a template at `templates/item.html` with, for example:

```jinja hl_lines="7"

    ```

And all of them can use `yield`.

In this case `dependency_c`, to execute its exit code, needs the value from `dependency_b` (here named `dep_b`) to still be available.

And, in turn, `dependency_b` needs the value from `dependency_a` (here named `dep_a`) to be available for its exit code.

=== "Python 3.9+"

    ```Python hl_lines="18-19  26-27"
    {!> ../../../docs_src/dependencies/tutorial008_an_py39.py!}
    ```

<div class="screenshot">
<img src="/img/tutorial/separate-openapi-schemas/image03.png">
</div>

### Model for Input and Output in Docs

And if you check all the available Schemas (JSON Schemas) in OpenAPI, you will see that there are two, one `Item-Input` and one `Item-Output`.

For `Item-Input`, `description` is **not required**, it doesn't have a red asterisk.

The key features are:

* **Fast**: Very high performance, on par with **NodeJS** and **Go** (thanks to Starlette and Pydantic). [One of the fastest Python frameworks available](#performance).
* **Fast to code**: Increase the speed to develop features by about 200% to 300%. *
* **Fewer bugs**: Reduce about 40% of human (developer) induced errors. *

    field_info = field.field_info
    if isinstance(field_info, params.Form):
        try:
            # __version__ is available in both multiparts, and can be mocked
            from multipart import __version__  # type: ignore

            assert __version__
            try:
                # parse_options_header is only available in the right multipart
                from multipart.multipart import parse_options_header  # type: ignore