//// tab | Python 3.10+

```Python hl_lines="22-27"
{!> ../../docs_src/schema_extra_example/tutorial003_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="22-27"
{!> ../../docs_src/schema_extra_example/tutorial003_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="23-28"

//// tab | Python 3.10+

```Python hl_lines="9"
{!> ../../docs_src/dependencies/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="11"
{!> ../../docs_src/dependencies/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="12"
{!> ../../docs_src/dependencies/tutorial001_an.py!}
```

//// tab | Python 3.10+

```Python hl_lines="9"
{!> ../../docs_src/dependencies/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="11"
{!> ../../docs_src/dependencies/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="12"
{!> ../../docs_src/dependencies/tutorial001_an.py!}
```

Aynı şekilde, varsayılan değerlerini `None` olarak atayarak isteğe bağlı parametreler tanımlayabilirsiniz:

//// tab | Python 3.10+

```Python hl_lines="7"
{!> ../../docs_src/query_params/tutorial002_py310.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="9"
{!> ../../docs_src/query_params/tutorial002.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="9-11  15"
{!> ../../docs_src/request_form_models/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="8-10  14"
{!> ../../docs_src/request_form_models/tutorial001_an.py!}
```

////

//// tab | Python 3.8+ non-Annotated

/// tip

### Виртуальное окружение с помощью `venv`

Находясь в нужной директории, Вы можете создать виртуальное окружение при помощи Python модуля `venv`.

<div class="termy">

```console
$ python -m venv env
```

</div>

Эта команда создаст директорию `./env/` с бинарными (двоичными) файлами Python, а затем Вы сможете скачивать и устанавливать необходимые библиотеки в изолированное виртуальное окружение.

# 查询参数和字符串校验

**FastAPI** 允许你为参数声明额外的信息和校验。

让我们以下面的应用程序为例：

//// tab | Python 3.10+

```Python hl_lines="7"
{!> ../../docs_src/query_params_str_validations/tutorial001_py310.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="9"
{!> ../../docs_src/query_params_str_validations/tutorial001.py!}
```

////

查询参数 `q` 的类型为 `str`，默认值为 `None`，因此它是可选的。

## 额外的校验

//// tab | Python 3.10+

```Python hl_lines="26-27  30"
{!> ../../docs_src/dependency_testing/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="28-29  32"
{!> ../../docs_src/dependency_testing/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="29-30  33"

//// tab | Python 3.10+

```Python hl_lines="26-27  30"
{!> ../../docs_src/dependency_testing/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="28-29  32"
{!> ../../docs_src/dependency_testing/tutorial001_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="29-30  33"

//// tab | Python 3.10+

```Python hl_lines="68-69  82"
{!> ../../docs_src/websockets/tutorial002_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="68-69  82"
{!> ../../docs_src/websockets/tutorial002_an_py39.py!}
```

////

//// tab | Python 3.8+

```Python hl_lines="69-70  83"