You could also use it to generate code automatically, for clients that communicate with your API. For example, frontend, mobile or IoT applications.

## Recap, step by step

### Step 1: import `FastAPI`

```Python hl_lines="1"
{!../../../docs_src/first_steps/tutorial001.py!}
```

`FastAPI` is a Python class that provides all the functionality for your API.

    As these keys may not necessarily be part of the OpenAPI specification, some OpenAPI tools, for example [the OpenAPI validator](https://validator.swagger.io/), may not work with your generated schema.

## Recap

You can use Pydantic's `Field` to declare extra validations and metadata for model attributes.

    This is not a limitation of **FastAPI**, it's part of the HTTP protocol.

## Recap

    This is not a limitation of **FastAPI**, it's part of the HTTP protocol.

## Recap

!!! info
    To declare cookies, you need to use `Cookie`, because otherwise the parameters would be interpreted as query parameters.

## Recap

But if you need to access variables and objects from the same **FastAPI** app, or you need to perform small background tasks (like sending an email notification), you can simply just use `BackgroundTasks`.

## Recap

```
X-Token: foo
X-Token: bar
```

The response would be like:

```JSON
{
    "X-Token values": [
        "bar",
        "foo"
    ]
}
```

## Recap

Declare headers with `Header`, using the same common pattern as `Query`, `Path` and `Cookie`.

    {!> ../../../docs_src/body_updates/tutorial002_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="35"
    {!> ../../../docs_src/body_updates/tutorial002.py!}
    ```

### Partial updates recap

In summary, to apply partial updates you would:

* (Optionally) use `PATCH` instead of `PUT`.
* Retrieve the stored data.
* Put that data in a Pydantic model.

=== "Python 3.8+ non-Annotated"

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

    ```Python hl_lines="30-32"
    {!> ../../../docs_src/security/tutorial002.py!}
    ```

## Recap

You can now get the current user directly in your *path operation function*.

We are already halfway there.

We just need to add a *path operation* for the user/client to actually send the `username` and `password`.

    ```Python hl_lines="1"
    async def needy_dependency(fresh_value: str = Depends(get_value, use_cache=False)):
        return {"fresh_value": fresh_value}
    ```

## Recap

Apart from all the fancy words used here, the **Dependency Injection** system is quite simple.

Just functions that look the same as the *path operation functions*.