### Use the `app.dependency_overrides` attribute

For these cases, your **FastAPI** application has an attribute `app.dependency_overrides`, it is a simple `dict`.

To override a dependency for testing, you put as a key the original dependency (a function), and as the value, your dependency override (another function).

And then **FastAPI** will call that override instead of the original dependency.

=== "Python 3.10+"

second_user_data = {
    "id": 4,
    "name": "Mary",
    "joined": "2018-11-30",
}

my_second_user: User = User(**second_user_data)
```

!!! info
    `**second_user_data` şu anlama geliyor:

    Key-Value çiftini direkt olarak  `second_user_data` dictionarysine kaydet , yaptığın şey buna eşit olacak: `User(id=4, name="Mary", joined="2018-11-30")`

### Editor desteği

İlk tip parametresi `dict` değerinin `key` değeri içindir.

İkinci parametre ise `dict` değerinin `value` değeri içindir:

```Python hl_lines="1  4"
{!../../../docs_src/python_types/tutorial008.py!}
```

Bu şu anlama gelir:

*  `prices` değişkeni `dict` tipindedir:
    *  `dict` değişkeninin `key` değeri  `str` tipindedir (herbir item'ın "name" değeri).

#### `Dict`

`dict`를 선언하려면 컴마로 구분된 2개의 파라미터가 필요합니다.

첫 번째 매개변수는 `dict`의 키(key)이고,

두 번째 매개변수는  `dict`의 값(value)입니다.

```Python hl_lines="1  4"
{!../../../docs_src/python_types/tutorial008.py!}
```

이 뜻은 아래와 같습니다:

* 변수 `prices`는 `dict`이다:
    * `dict`의 키(key)는 `str`타입이다. (각 아이템의 이름(name))
    * `dict`의 값(value)는 `float`타입이다. (각 아이템의 가격(price))

#### `Optional`

{!../../../docs_src/sql_databases/sql_app/models.py!}
```

When accessing the attribute `items` in a `User`, as in `my_user.items`, it will have a list of `Item` SQLAlchemy models (from the `items` table) that have a foreign key pointing to this record in the `users` table.

When you access `my_user.items`, SQLAlchemy will actually go and fetch the items from the database in the `items` table and populate them here.

---

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.

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).

...Python has a little special syntax for that.

Pass `*`, as the first parameter of the function.

Python won't do anything with that `*`, but it will know that all the following parameters should be called as keyword arguments (key-value pairs), also known as <abbr title="From: K-ey W-ord Arg-uments"><code>kwargs</code></abbr>. Even if they don't have a default value.

```Python hl_lines="7"
{!../../../docs_src/path_params_numeric_validations/tutorial003.py!}

# Settings and Environment Variables

In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.

Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.

For this reason it's common to provide them in environment variables that are read by the application.

## Environment Variables

!!! tip