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

Por baixo dos panos, o código `open("./somefile.txt")` cria um objeto que é chamado de "Gerenciador de Contexto".

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

Internamente, `open("./somefile.txt")` crea un objeto llamado "Context Manager".

Cuando el bloque `with` termina, se asegura de cerrar el archivo, incluso si hubo excepciones.

	// Should only be modified before any calls are made.
	MaxErrResponseSize int64

	// Avoid metrics update if set to true
	NoMetrics bool

	// TraceOutput will print debug information on non-200 calls if set.
	TraceOutput io.Writer // Debug trace output

	httpClient *http.Client
	url        *url.URL
	auth       func() string

	sync.RWMutex // mutex for lastErr

-size:1.75rem!important}.fs-4{font-size:1.5rem!important}}@media print{.d-print-inline{display:inline!important}.d-print-inline-block{display:inline-block!important}.d-print-block{display:block!important}.d-print-grid{display:grid!important}.d-print-inline-grid{display:inline-grid!important}.d-print-table{display:table!important}.d-print-table-row{display:table-row!important}.d-print-table-cell{display:table-cell!important}.d-print-flex{display:flex!important}.d-print-inline-flex{display:inline-...

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

Im Hintergrund erstellt das `open("./somefile.txt")` ein Objekt, das als „Kontextmanager“ bezeichnet wird.

	}

	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.

////

## 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

////

### 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。