# Variables de Entorno { #environment-variables }

/// tip | Consejo

Si ya sabes qué son las "variables de entorno" y cómo usarlas, siéntete libre de saltarte esto.

///

Una variable de entorno (también conocida como "**env var**") es una variable que vive **fuera** del código de Python, en el **sistema operativo**, y podría ser leída por tu código de Python (o por otros programas también).

# Environment Variables { #environment-variables }

/// tip

If you already know what "environment variables" are and how to use them, feel free to skip this.

///

An environment variable (also known as "**env var**") is a variable that lives **outside** of the Python code, in the **operating system**, and could be read by your Python code (or by other programs as well).

   *
   * @param formal The type whose type variables or itself is mapped to other type(s). It's almost
   *     always a bug if {@code formal} isn't a type variable and contains no type variable. Make
   *     sure you are passing the two parameters in the right order.
   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet

### Classes en tant que types

Vous pouvez aussi déclarer une classe comme type d'une variable.

Disons que vous avez une classe `Person`, avec une variable `name` :

{*../../docs_src/python_types/tutorial010.py hl[1:3] *}


Vous pouvez ensuite déclarer une variable de type `Person` :

{*../../docs_src/python_types/tutorial010.py hl[6] *}

   *
   * @param formal The type whose type variables or itself is mapped to other type(s). It's almost
   *     always a bug if {@code formal} isn't a type variable and contains no type variable. Make
   *     sure you are passing the two parameters in the right order.
   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet

        return URL_QUEUE_SERVICE_THREAD_LOCAL.get();
    }

    /**
     * Sets the UrlQueueService instance to the thread-local variable.
     * If the provided UrlQueueService is null, it removes the current instance from the thread-local variable.
     *
     * @param urlQueueService the UrlQueueService instance to be set, or null to remove the current instance
     */

#### Liste { #list }

Definieren wir zum Beispiel eine Variable, die eine `list` von `str` – eine Liste von Strings – sein soll.

Deklarieren Sie die Variable mit der gleichen Doppelpunkt-Syntax (`:`).

Als Typ nehmen Sie `list`.

Da die Liste ein Typ ist, welcher innere Typen enthält, werden diese von eckigen Klammern umfasst:

:end
@rem End local scope for the variables with windows NT shell
if %ERRORLEVEL% equ 0 goto mainEnd

:fail
rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
rem the _cmd.exe /c_ return code!
set EXIT_CODE=%ERRORLEVEL%
if %EXIT_CODE% equ 0 set EXIT_CODE=1
if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
exit /b %EXIT_CODE%

:mainEnd
if "%OS%"=="Windows_NT" endlocal

   * add the suppression to the whole method (which turns off checking for a large section of code),
   * or extract a variable, and put the suppression on that. However, a local variable typically
   * doesn't work: Because nullness analyses typically infer the nullness of local variables,
   * there's no way to assign a {@code @Nullable T} to a field {@code T foo;} and instruct the

   * add the suppression to the whole method (which turns off checking for a large section of code),
   * or extract a variable, and put the suppression on that. However, a local variable typically
   * doesn't work: Because nullness analyses typically infer the nullness of local variables,
   * there's no way to assign a {@code @Nullable T} to a field {@code T foo;} and instruct the