<div class="termy">

```console
// Here we don't set the env var yet
$ python main.py

// As we didn't set the env var, we get the default value

Hello World from Python

// But if we create an environment variable first
$ export MY_NAME="Wade Wilson"

// And then call the program again
$ python main.py

// Now it can read the environment variable

Hello Wade Wilson from Python
```

</div>

```console
// Hier stellen we de omgevingsvariabelen nog niet in
$ python main.py

// Omdat we de omgevingsvariabelen niet hebben ingesteld, krijgen we de standaardwaarde

Hello World from Python

// Maar als we eerst een omgevingsvariabele aanmaken
$ export MY_NAME="Wade Wilson"

// en het programma dan opnieuw aanroepen
$ python main.py

// kan het de omgevingsvariabele nu wel uitlezen

Hello Wade Wilson from Python

# Query Parameters { #query-parameters }

When you declare other function parameters that are not part of the path parameters, they are automatically interpreted as "query" parameters.

{* ../../docs_src/query_params/tutorial001.py hl[9] *}

The query is the set of key-value pairs that go after the `?` in a URL, separated by `&` characters.

For example, in the URL:

```
http://127.0.0.1:8000/items/?skip=0&limit=10
```

🥇, ✍ 🌐 👆 **FastAPI** 🈸 🛎:

{* ../../docs_src/extending_openapi/tutorial001.py hl[1,4,7:9] *}

### 🏗 🗄 🔗

⤴️, ⚙️ 🎏 🚙 🔢 🏗 🗄 🔗, 🔘 `custom_openapi()` 🔢:

{* ../../docs_src/extending_openapi/tutorial001.py hl[2,15:20] *}

### 🔀 🗄 🔗

🔜 👆 💪 🚮 📄 ↔, ❎ 🛃 `x-logo` `info` "🎚" 🗄 🔗:

{* ../../docs_src/extending_openapi/tutorial001.py hl[21:23] *}

### 💾 🗄 🔗

```
.
├── app
│   ├── __init__.py
│   ├── main.py
│   ├── dependencies.py
│   └── routers
│   │   ├── __init__.py
│   │   ├── items.py
│   │   └── users.py
│   └── internal
│       ├── __init__.py
│       └── admin.py
```

/// tip | Consejo

Hay varios archivos `__init__.py`: uno en cada directorio o subdirectorio.

## `Header` importieren

Importieren Sie zuerst `Header`:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[3] *}

## `Header`-Parameter deklarieren

Dann deklarieren Sie Ihre Header-Parameter, auf die gleiche Weise, wie Sie auch `Path`-, `Query`-, und `Cookie`-Parameter deklarieren.

Dependências podem declarar requisitos de requisições (como cabeçalhos) ou outras subdependências:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[8,13] *}

### Levantando exceções

Essas dependências podem levantar exceções, da mesma forma que dependências comuns:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[10,15] *}

### Valores de retorno

E elas também podem ou não retornar valores, eles não serão utilizados.

```
.
├── app
│   ├── __init__.py
│   ├── main.py
│   ├── dependencies.py
│   └── routers
│   │   ├── __init__.py
│   │   ├── items.py
│   │   └── users.py
│   └── internal
│       ├── __init__.py
│       └── admin.py
```

/// tip | Dica

Existem vários arquivos `__init__.py` presentes em cada diretório ou subdiretório.

{* ../../docs_src/dependencies/tutorial002_an_py310.py hl[11:15] *}

Presta atención al método `__init__` usado para crear la instance de la clase:

{* ../../docs_src/dependencies/tutorial002_an_py310.py hl[12] *}

...tiene los mismos parámetros que nuestros `common_parameters` anteriores:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8] *}

Und Sie können auch Body-Parameter als optional kennzeichnen, indem Sie den Defaultwert auf `None` setzen:

{* ../../docs_src/body_multiple_params/tutorial001_an_py310.py hl[18:20] *}

/// note | Hinweis

Beachten Sie, dass in diesem Fall das `item`, welches vom Body genommen wird, optional ist. Da es `None` als Defaultwert hat.

///

## Mehrere Body-Parameter