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

Underneath, the `open("./somefile.txt")` creates an object that is called a "Context Manager".

When the `with` block finishes, it makes sure to close the file, even if there were exceptions.

////

## Pythonで環境変数を読み取る

環境変数をPythonの**外側**、ターミナル（や他の方法）で作成し、**Python内で読み取る**こともできます。

例えば、以下のような`main.py`ファイルを用意します:

```Python hl_lines="3"
import os

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

/// tip

<a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> の第2引数は、デフォルトで返される値を指定します。

# protobuf dependencies ourselves. By default this value is false, but some 
# projects enable it, which we don't want here.
# common --define=use_fast_cpp_protos=true

# Make Bazel print out all options from rc files.
common --announce_rc

# TODO(mihaimaruseac): Document this option or remove if no longer needed
common --define=grpc_no_ares=true

	}

	lockRetryBackOff = backoffWait(
		lockRetryMinInterval,
		100*time.Millisecond,
		5*time.Second,
	)
}

func log(format string, data ...any) {
	if dsyncLog {
		console.Printf(format, data...)
	}
}

const (
	// dRWMutexAcquireTimeout - default tolerance limit to wait for lock acquisition before.
	drwMutexAcquireTimeout = 1 * time.Second // 1 second.

  If the `DeclarativeValidationTakeover` feature gate was enabled, declarative validation was the primary source of errors for migrated fields. ([#133013](https://github.com/kubernetes/kubernetes/pull/133013), [@aaron-prindle](https://github.com/aaron-prindle)) [SIG API Machinery and Auth]

        the environment variable `TF_DETERMINISTIC_OPS` to `"true"` or `"1"`.
*   `tf.print`:
    *   Bug fix in `tf.print()` with `OrderedDict` where if an `OrderedDict`
        didn't have the keys sorted, the keys and values were not being printed
        in accordance with their correct mapping.
*   `tf.train.Checkpoint`:

////

### 在 Python 中读取环境变量

您还可以在 Python 之外的地方（例如终端中或使用任何其他方法）创建环境变量，然后在 Python 中读取它们。

例如，您可以有一个名为 `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

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

- Kubeadm: Added error printing during retries related to the `WaitForAllControlPlaneComponents` functionality at verbosity level 5. ([#134433](https://github.com/kubernetes/kubernetes/pull/134433), [@neolit123](https://github.com/neolit123))

また、何らかの方法で例外を使用することもできますが、**FastAPI** から同じデフォルトの例外ハンドラを使用することもできます。

デフォルトの例外ハンドラを`fastapi.exception_handlers`からインポートして再利用することができます:

{* ../../docs_src/handling_errors/tutorial006.py hl[2,3,4,5,15,21] *}

この例では、非常に表現力のあるメッセージでエラーを`print`しています。

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

내부적으로 `open("./somefile.txt")` 는 "컨텍스트 관리자(Context Manager)"라고 불리는 객체를 생성합니다.

`with` 블록이 끝나면, 예외가 발생했더라도 파일을 닫도록 보장합니다.