你也可以在 Python **之外**的终端中创建环境变量（或使用任何其他方法），然后在 Python 中**读取**它们。

例如，你可以创建一个名为 `main.py` 的文件，其中包含以下内容：

```Python hl_lines="3"
import os

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

/// tip | 提示

第二个参数是 [`os.getenv()`](https://docs.python.org/3.8/library/os.html#os.getenv) 的默认返回值。

如果没有提供，默认值为 `None`，这里我们提供 `"World"` 作为默认值。

///

                        <groupId>org.springframework.boot</groupId>
                        <artifactId>spring-boot-starter-parent</artifactId>
                        <version>3.0.0</version>
                        <relativePath/>
                    </parent>
                    <artifactId>my-spring-app</artifactId>
                    <!-- No explicit groupId or version - would inherit from parent -->

}

func (target *MQTTTarget) initMQTT() error {
	args := target.args

	// Using hex here, to make sure we avoid 23
	// character limit on client_id according to
	// MQTT spec.
	clientID := fmt.Sprintf("%x", time.Now().UnixNano())

	options := mqtt.NewClientOptions().
		SetClientID(clientID).
		SetCleanSession(true).
		SetUsername(args.User).
		SetPassword(args.Password).

		}
		w.export(pkg)

		if *updateGolden {
			os.Remove(goldenFile)
			f, err := os.Create(goldenFile)
			if err != nil {
				t.Fatal(err)
			}
			for _, feat := range w.Features() {
				fmt.Fprintf(f, "%s\n", feat)
			}
			f.Close()
		}

		bs, err := os.ReadFile(goldenFile)
		if err != nil {
			t.Fatalf("opening golden.txt for package %q: %v", fi.Name(), err)
		}

			}
			return written, nil
		}
	}
}

// SafeClose safely closes any channel of any type
func SafeClose[T any](c chan<- T) {
	if c != nil {
		close(c)
		return
	}
	// Print stack to check who is sending `c` as `nil`
	// without crashing the server.
	debug.PrintStack()

      echo "[DEBUG] JvmConfigParser exit code: $parser_exit" >&2
      echo "[DEBUG] JvmConfigParser output: $parser_output" >&2
    fi

    if [ $parser_exit -ne 0 ]; then
      # Parser failed - print comprehensive error information
      echo "ERROR: JvmConfigParser failed with exit code $parser_exit" >&2
      echo "  jvm.config path: $1" >&2
      echo "  Maven basedir: $MAVEN_PROJECTBASEDIR" >&2

```

接著呼叫：

```Python
user_dict = user_in.model_dump()
```

此時變數 `user_dict` 會是一個承載資料的 `dict`（也就是 `dict`，而非 Pydantic 模型物件）。

若再呼叫：

```Python
print(user_dict)
```

我們會得到一個 Python `dict`：

```Python
{
    'username': 'john',
    'password': 'secret',
    'email': '******@****.***',
    'full_name': None,
}
```

        prp.store(out, header);
    }

    /**
     * List the properties in the <code>Config</code>.
     *
     * @param out the print stream to write the properties to
     * @throws IOException if an I/O error occurs
     */

    public static void list(final PrintStream out) throws IOException {
        prp.list(out);
    }

    /**

```python
from typing import Any


def some_function(data: Any):
    print(data)
```

### Generic types { #generic-types }

Some types can take "type parameters" in square brackets, to define their internal types, for example a "list of strings" would be declared `list[str]`.

    @get:Optional
    @get:Option(option = "fix", description = "When enabled, will write the correct computed runtimes back to the build files")
    abstract val fix: Property<Boolean>

    /**
     * If enabled, prints extra details describing why a target runtime declaration is invalid.
     */
    @get:Input
    @get:Optional