Las variables de entorno pueden ser útiles para manejar **configuraciones** de aplicaciones, como parte de la **instalación** de Python, etc.

## Crear y Usar Variables de Entorno { #create-and-use-env-vars }

Puedes **crear** y usar variables de entorno en la **shell (terminal)**, sin necesidad de Python:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console

    CharBuffer empty = CharBuffer.wrap("");
    assertEquals(0, CharStreams.exhaust(empty));
    assertEquals(0, empty.remaining());
  }

  public void testNullWriter() throws Exception {
    // create a null writer
    Writer nullWriter = CharStreams.nullWriter();
    // write to the writer
    nullWriter.write('n');
    String test = "Test string for NullWriter";
    nullWriter.write(test);

    input.addListener(output, rejectionPropagatingExecutor(executor, output));
    return output;
  }

  static <I extends @Nullable Object, O extends @Nullable Object> ListenableFuture<O> create(
      ListenableFuture<I> input, Function<? super I, ? extends O> function, Executor executor) {
    TransformFuture<I, O> output = new TransformFuture<>(input, function);

    CharBuffer empty = CharBuffer.wrap("");
    assertEquals(0, CharStreams.exhaust(empty));
    assertEquals(0, empty.remaining());
  }

  public void testNullWriter() throws Exception {
    // create a null writer
    Writer nullWriter = CharStreams.nullWriter();
    // write to the writer
    nullWriter.write('n');
    String test = "Test string for NullWriter";
    nullWriter.write(test);

///

### Das `Settings`-Objekt erstellen { #create-the-settings-object }

Importieren Sie `BaseSettings` aus Pydantic und erstellen Sie eine Unterklasse, ganz ähnlich wie bei einem Pydantic-Modell.

	// If false only main directory will be scanned.
	// Should always be true if Separator is n SlashSeparator.
	Recursive bool

	// Separator to use.
	Separator string

	// Create indicates that the lister should not attempt to load an existing cache.
	Create bool

	// Include pure directories.
	IncludeDirectories bool

	// Transient is set if the cache is transient due to an error or being a reserved bucket.

					"abcd",
				},
				// Date
				queryTime,
				// Expires.
				100 * time.Second,
			},
			expectedErrCode: ErrNone,
		},

		// Test case - 9.
		// Test case with value greater than 604800 in X-Amz-Expires header.
		{
			inputQueryKeyVals: []string{
				// valid  "X-Amz-Algorithm" header.
				"X-Amz-Algorithm", signV4Algorithm,
				// valid  "X-Amz-Credential" header.

        final Tuple3<String, String, String> task = new Tuple3<>(getName(), thumbnailId, path);
        if (logger.isDebugEnabled()) {
            logger.debug("Create thumbnail task: {}", task);
        }
        return task;
    }

    /**
     * Sets the directory name length for thumbnail storage.
     * @param directoryNameLength The directory name length.
     */

Umgebungsvariablen können nützlich sein, um **Einstellungen** der Anwendung zu handhaben, als Teil der **Installation** von Python usw.

## Umgebungsvariablen erstellen und verwenden { #create-and-use-env-vars }

Sie können Umgebungsvariablen in der **Shell (Terminal)** erstellen und verwenden, ohne Python zu benötigen:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console

## Как это выглядит { #how-it-looks }

Сначала просто воспользуемся кодом и посмотрим, как он работает, а затем вернемся и разберемся, что происходит.

## Создание `main.py` { #create-main-py }

Скопируйте пример в файл `main.py`:

{* ../../docs_src/security/tutorial001_an_py39.py *}

## Запуск { #run-it }

/// info | Дополнительная информация