The parameter is available only for compatibility.
            """
        ),
    ] = ...,
    *,
    default_factory: Annotated[
        Union[Callable[[], Any], None],
        Doc(
            """
            A callable to generate the default value.

            This doesn't affect `Path` parameters as the value is always required.
            The parameter is available only for compatibility.

import warnings
from enum import Enum
from typing import Any, Callable, Dict, List, Optional, Sequence, Union

from fastapi.openapi.models import Example
from pydantic.fields import FieldInfo
from typing_extensions import Annotated, deprecated

from ._compat import PYDANTIC_V2, PYDANTIC_VERSION, Undefined

_Unset: Any = Undefined


class ParamTypes(Enum):
    query = "query"
    header = "header"
    path = "path"

# Abhängigkeiten – `Depends()` und `Security()`

## `Depends()`

Abhängigkeiten werden hauptsächlich mit der speziellen Funktion `Depends()` behandelt, die ein Callable entgegennimmt.

Hier finden Sie deren Referenz und Parameter.

Sie können sie direkt von `fastapi` importieren:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

from typing import Any, Callable, List, Optional, Sequence

from fastapi._compat import ModelField
from fastapi.security.base import SecurityBase


class SecurityRequirement:
    def __init__(
        self, security_scheme: SecurityBase, scopes: Optional[Sequence[str]] = None
    ):
        self.security_scheme = security_scheme
        self.scopes = scopes


class Dependant:
    def __init__(
        self,
        *,

The `oauth2_scheme` variable is an instance of `OAuth2PasswordBearer`, but it is also a "callable".

It could be called as:

```Python
oauth2_scheme(some, parameters)
```

So, it can be used with `Depends`.

### Use it

* Fix support for callable class dependencies with `yield`. PR [#1365](https://github.com/tiangolo/fastapi/pull/1365) by [@mrosales](https://github.com/mrosales).

But we want to be able to parameterize that fixed content.

## A "callable" instance

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

To do that, we declare a method `__call__`:

=== "Python 3.9+"

    ```Python hl_lines="12"

Eine Python-Klasse ist also auch ein **Callable**.

Darum können Sie in **FastAPI** auch eine Python-Klasse als Abhängigkeit verwenden.

Was FastAPI tatsächlich prüft, ist, ob es sich um ein „Callable“ (Funktion, Klasse oder irgendetwas anderes) handelt und ob die Parameter definiert sind.

            ),
        ] = State()
        self.dependency_overrides: Annotated[
            Dict[Callable[..., Any], Callable[..., Any]],
            Doc(
                """
                A dictionary with overrides for the dependencies.

                Each key is the original dependency callable, and the value is the
                actual dependency that should be called.

# 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()`