Örneğin `main.py` adında bir dosyanız şöyle olabilir:

```Python hl_lines="3"
import os

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

/// tip | İpucu

[`os.getenv()`](https://docs.python.org/3.8/library/os.html#os.getenv) fonksiyonunun ikinci argümanı, bulunamadığında döndürülecek varsayılan (default) değerdir.

Verilmezse varsayılan olarak `None` olur; burada varsayılan değer olarak `"World"` verdik.

///

   <span style="background-color:#007166"><font color="#D3D7CF"> server </font></span>  Documentation at <font color="#729FCF"><u style="text-decoration-style:solid">http://127.0.0.1:8000/docs</u></font>

      <span style="background-color:#007166"><font color="#D3D7CF"> tip </font></span>  Running in development mode, for production use:
             <b>fastapi run</b>

             Logs:

 [advanced_profiling_bug]: https://issuetracker.google.com/issues/135141615
 [japicmp]: https://github.com/siom79/japicmp
 [japicmp_gradle]: https://github.com/melix/japicmp-gradle-plugin
 [java_sams]: https://kotlinlang.org/docs/reference/java-interop.html#sam-conversions
 [kotlin_sams]: https://youtrack.jetbrains.com/issue/KT-11129
 [mockito]: https://site.mockito.org/
 [proguard_problems]: https://github.com/square/okhttp/issues/5167

					<excludes>
						<exclude>pom.xml</exclude>
						<exclude>breaking-changes.xml</exclude>
						<exclude>*.md</exclude>
						<exclude>*.sh</exclude>
						<exclude>build.properties</exclude>
						<exclude>docs/**</exclude>
						<exclude>src/test/resources/**</exclude>
						<exclude>**/*.idl</exclude>
						<exclude>**/*.css</exclude>
						<exclude>.*</exclude>
						<exclude>.*/**</exclude>

/// info

You can read more about the Starlette `lifespan` handlers in [Starlette's  Lifespan' docs](https://www.starlette.dev/lifespan/).

Including how to handle lifespan state that can be used in other areas of your code.

///

## Sub Applications { #sub-applications }

```Python hl_lines="3"
import os

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

/// tip

The second argument to [`os.getenv()`](https://docs.python.org/3.8/library/os.html#os.getenv) is the default value to return.

If not provided, it's `None` by default, here we provide `"World"` as the default value to use.

///

Then you could call that Python program:

```Python hl_lines="3"
import os

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

/// tip | Astuce

Le deuxième argument de [`os.getenv()`](https://docs.python.org/3.8/library/os.html#os.getenv) est la valeur par défaut à retourner.

S'il n'est pas fourni, c'est `None` par défaut ; ici, nous fournissons `"World"` comme valeur par défaut à utiliser.

///

   <span style="background-color:#007166"><font color="#D3D7CF"> server </font></span>  Documentation at <font color="#729FCF"><u style="text-decoration-style:solid">http://127.0.0.1:8000/docs</u></font>

      <span style="background-color:#007166"><font color="#D3D7CF"> tip </font></span>  Running in development mode, for production use:
             <b>fastapi run</b>

             Logs:

- 編輯器支援（自動完成等），即使是巢狀模型
- 資料轉換
- 資料驗證
- 自動產生文件

## 特殊型別與驗證 { #special-types-and-validation }

除了 `str`、`int`、`float` 等一般的單一型別外，你也可以使用繼承自 `str` 的更複雜單一型別。

若要查看所有可用選項，請參閱 [Pydantic 的型別總覽](https://docs.pydantic.dev/latest/concepts/types/)。你會在下一章看到一些範例。

例如，在 `Image` 模型中有一個 `url` 欄位，我們可以將其宣告為 Pydantic 的 `HttpUrl`，而不是 `str`：

{* ../../docs_src/body_nested_models/tutorial005_py310.py hl[2,8] *}

                || exception.getMessage().toLowerCase().contains("process"));
    }

    @Test
    @DisplayName("Should handle DOS error codes")
    void testDOSErrorCodes() {
        // Given
        int dosError = 0x00020002; // File not found from DOS_ERROR_CODES

        // When