////

## 在 Python 中读取环境变量

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

第二个参数是 <a href="https://docs.python.org/zh-cn/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> 的默认返回值。

```

そして呼び出すと:

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

これで変数`user_dict`のデータを持つ`dict`ができました。（これはPydanticモデルのオブジェクトの代わりに`dict`です）。

そして呼び出すと:

```Python
print(user_dict)
```

以下のようなPythonの`dict`を得ることができます:

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

			Key:   target.MqttBroker,
			Value: cfg.Broker.String(),
		},
		config.KV{
			Key:   target.MqttTopic,
			Value: cfg.Topic,
		},
		config.KV{
			Key:   target.MqttQoS,
			Value: fmt.Sprintf("%d", cfg.QoS),
		},
		config.KV{
			Key:   target.MqttUsername,
			Value: cfg.User,
		},
		config.KV{
			Key:   target.MqttPassword,
			Value: cfg.Password,
		},
		config.KV{

    static class ValueHolder {
      @Nullable String name;
      @Nullable Object value;
      @Nullable ValueHolder next;
    }

    /**
     * Holder object for values that cannot be null or empty (will be printed unconditionally). This
     * helps to shortcut most calls to isEmpty(), which is important because the check for emptiness
     * is relatively expensive. Use a subtype so this also doesn't need any extra storage.
     */

and then replaces each occurrence of a type C.xxx with _C_xxx.

If xxx is data, cgo arranges for C.xxx to refer to the C variable,
with the type translated as described above.  To do this, cgo must
introduce a Go variable that points at the C variable (the linker can
be told to initialize this pointer).  For example, if the gmp library
provided

	mpz_t zero;

then cgo would rewrite a reference to C.zero by introducing

	var _C_zero *C.mpz_t

             * for whatever reason. I copy over the uid here so it appears correct
             * in logging output. Logging of andx segments of messages inadvertantly
             * print header information because of the way toString always makes a
             * super.toString() call(see toString() at the end of all smbs classes).
             */

            this.andx.uid = this.uid;

2018/12/26 17:49:36 listening on http://localhost:8888/
```

This will open the login page of keycloak, upon successful login, STS credentials along with any buckets discovered using the credentials will be printed on the screen, for example:

```
{
  "buckets": [
    "bucket-x"
  ],
  "credentials": {
    "AccessKeyID": "6N2BALX7ELO827DXS3GK",

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

その後の`open("./somefile.txt")`は「コンテキストマネージャ」と呼ばれるオブジェクトを作成します。

`with`ブロックが終了すると、例外があったとしてもファイルを確かに閉じます。

`yield`を依存関係を作成すると、**FastAPI** は内部的にそれをコンテキストマネージャに変換し、他の関連ツールと組み合わせます。

                if (parent.getRelativePath() == null || parent.getRelativePath().length() <= 0) {
                    buffer.append(" and 'parent.relativePath' points at no local POM");
                } else {
                    buffer.append(" and 'parent.relativePath' points at wrong local POM");
                }
            }

            problems.add(new ModelProblemCollectorRequest(Severity.FATAL, Version.BASE)

        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);
    }

    /**