# 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).

#### Listas

Por ejemplo, vamos a definir una variable para que sea una `list` compuesta de `str`.

De `typing`, importa `List` (con una `L` mayúscula):

```Python hl_lines="1"
{!../../docs_src/python_types/tutorial006.py!}
```

Declara la variable con la misma sintaxis de los dos puntos (`:`).

Pon `List` como el tipo.

### 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] *}

import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.annotations.Nullable;

/**
 * The Interpolator service provides methods for variable substitution in strings and maps.
 * It allows for the replacement of placeholders (e.g., ${variable}) with their corresponding values.
 *
 * @since 4.0.0
 */
@Experimental
public interface Interpolator extends Service {

    /**

#### Liste

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

//// tab | Python 3.9+

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

Als Typ nehmen Sie `list`.

<p>
Computer architectures may require memory addresses to be <i>aligned</i>;
that is, for addresses of a variable to be a multiple of a factor,
the variable's type's <i>alignment</i>.  The function <code>Alignof</code>
takes an expression denoting a variable of any type and returns the
alignment of the (type of the) variable in bytes.  For a variable
<code>x</code>:
</p>

<pre>
uintptr(unsafe.Pointer(&amp;x)) % unsafe.Alignof(x) == 0

	}
}

func serverHandleEnvVars() {
	var err error
	if globalBrowserEnabled {
		if redirectURL := env.Get(config.EnvBrowserRedirectURL, ""); redirectURL != "" {
			u, err := xnet.ParseHTTPURL(redirectURL)
			if err != nil {
				logger.Fatal(err, "Invalid MINIO_BROWSER_REDIRECT_URL value in environment variable")
			}

#### List

For example, let's define a variable to be a `list` of `str`.

//// tab | Python 3.9+

Declare the variable, with the same colon (`:`) syntax.

As the type, put `list`.

As the list is a type that contains some internal types, you put them in square brackets:

# Note: this file gets sourced in utilities/setup.sh, which has "set -u"
# (error on undefined variables). This ensures that (a) every TFCI variable
# has an explicit default value, and (b) no script can accidentally use a
# variable that doesn't exist. Please keep this list in alphabetical order.
#
# Find usage in scripts with e.g.:
#   cd ci/official

So, if you have another file `importer.py` with:

```Python
from myapp import app

# Some more code
```

in that case, the automatically created variable inside of `myapp.py` will not have the variable `__name__` with a value of `"__main__"`.

So, the line:

```Python
    uvicorn.run(app, host="0.0.0.0", port=8000)
```

will not be executed.

/// info