```Python
q: Union[str, None] = None
```

Or in Python 3.10 and above:

```Python
q: str | None = None
```

For example:

//// tab | Python 3.10+

```Python hl_lines="28"
{!> ../../docs_src/body_multiple_params/tutorial004_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="28"

```Python
q: Union[str, None] = None
```

Oder in Python 3.10 und darüber:

```Python
q: str | None = None
```

Zum Beispiel:

//// tab | Python 3.10+

```Python hl_lines="27"
{!> ../../docs_src/body_multiple_params/tutorial004_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="27"

//// tab | Python 3.10+

```Python hl_lines="8-9"
{!> ../../docs_src/dependencies/tutorial005_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="8-9"
{!> ../../docs_src/dependencies/tutorial005_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="9-10"
{!> ../../docs_src/dependencies/tutorial005_an.py!}
```

//// tab | Python 3.10+

```Python hl_lines="63-66"
{!> ../../docs_src/security/tutorial005_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="63-66"
{!> ../../docs_src/security/tutorial005_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="64-67"
{!> ../../docs_src/security/tutorial005_an.py!}
```

////

Öncelikle, `Cookie`'yi projenize dahil edin:

//// tab | Python 3.10+

```Python hl_lines="3"
{!> ../../docs_src/cookie_params/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="3"
{!> ../../docs_src/cookie_params/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="3"
{!> ../../docs_src/cookie_params/tutorial001_an.py!}
```

//// tab | Python 3.10+

```Python hl_lines="1  3  12-16"
{!> ../../docs_src/extra_data_types/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="1  3  12-16"
{!> ../../docs_src/extra_data_types/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="1  3  13-17"

//// tab | Python 3.10+

```Python hl_lines="9-14  18"
{!> ../../docs_src/header_param_models/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="9-14  18"
{!> ../../docs_src/header_param_models/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="10-15  19"

Es sollte eine `list`e von `Depends()` sein:

//// tab | Python 3.9+

```Python hl_lines="19"
{!> ../../docs_src/dependencies/tutorial006_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="18"
{!> ../../docs_src/dependencies/tutorial006_an.py!}
```

////

//// tab | Python 3.8 nicht annotiert

/// tip | "Tipp"

```

</div>

////

## Ler Variáveis de Ambiente no Python

Você também pode criar variáveis de ambiente **fora** do Python, no terminal (ou com qualquer outro método) e depois **lê-las no Python**.

Por exemplo, você poderia ter um arquivo `main.py` com:

```Python hl_lines="3"
import os

name = os.getenv("MY_NAME", "World")
print(f"Hello {name} from Python")
```

/// tip | "Dica"

///

//// tab | Python 3.10+

```Python hl_lines="1  14-15  18-20  33"
{!> ../../docs_src/extra_models/tutorial003_py310.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="1  14-15  18-20  33"
{!> ../../docs_src/extra_models/tutorial003.py!}
```

////

## 模型列表

使用同样的方式也可以声明由对象列表构成的响应。

为此，请使用标准的 Python `typing.List`：

//// tab | Python 3.9+