# Dependencies - `Depends()` and `Security()`

## `Depends()`

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

        // Expected type of `expression` is `T`
        val function = expression.unwrapQualified<KtFunction> { function, expr -> function.bodyExpression == expr } ?: return null
        if (function.bodyBlockExpression != null) {
            // Given `fun f(...): R { blockExpression }`, `{ blockExpression }` is mapped to the enclosing anonymous function,

In this case, we pass a dependency function `get_current_active_user` to `Security` (the same way we would do with `Depends`).

But we also pass a `list` of scopes, in this case with just one scope: `items` (it could have more).

And the dependency function `get_current_active_user` can also declare sub-dependencies, not only with `Depends` but also with `Security`. Declaring its own sub-dependency function (`get_current_user`), and more scope requirements.

}

/**
 * Returns whether the function uses its body as an expression (i.e., the function uses the result value of the expression) or not.
 *
 * Named functions do not consider their bodies used if
 *  - the function body is a block e.g., `fun foo(): Int { return bar }` or
 *  - the function itself returns Unit
 */

# Get Current User

In the previous chapter the security system (which is based on the dependency injection system) was giving the *path operation function* a `token` as a `str`:

=== "Python 3.9+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/security/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/security/tutorial001_an.py!}
    ```

=== "Python 3.8+ non-Annotated"

sequenceDiagram

participant code as Code
participant function as say_hi()
participant execute as Execute function

    rect rgba(0, 255, 0, .1)
        code ->> function: say_hi(name="Camila")
        function ->> execute: 执行函数代码
        execute ->> code: 返回结果
    end

    rect rgba(0, 255, 255, .1)
        code ->> function: say_hi(name="Camila")
        function ->> code: 返回存储的结果
    end

     * For example, `foo.Foo.bar` may only refer to the extension callable `bar` with
     * a `foo.Foo` receiver type, and this function will only look for such combinations.
     *
     * N.B. This function only searches for extension callables qualified by receiver types!
     * It does not try to resolve fully qualified or member functions, because they are dealt
     * with by the other parts of [KDocReferenceResolver].
     */

The new [ParseCookie] function parses a Cookie header value and
returns all the cookies which were set in it. Since the same cookie
name can appear multiple times the returned Values can contain
more than one value for a given key.

The new [ParseSetCookie] function parses a Set-Cookie header value and

        resolveFragmentOfCall: Boolean
    ): List<KtCallCandidateInfo> {
        // If a function call is resolved to an implicit invoke call, the FirImplicitInvokeCall will have the `invoke()` function as the
        // callee and the variable as the explicit receiver. To correctly get all candidates, we need to get the original function
        // call's explicit receiver (if there is any) and callee (i.e., the variable).

    ```

## Request body + path parameters

You can declare path parameters and request body at the same time.

**FastAPI** will recognize that the function parameters that match path parameters should be **taken from the path**, and that function parameters that are declared to be Pydantic models should be **taken from the request body**.

=== "Python 3.10+"

    ```Python hl_lines="15-16"