# 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

   *
   * @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

#### List { #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:

	}
}

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")
			}

////

That command will create or modify some [environment variables](environment-variables.md){.internal-link target=_blank} that will be available for the next commands.

One of those variables is the `PATH` variable.

/// tip

You can learn more about the `PATH` environment variable in the [Environment Variables](environment-variables.md#path-environment-variable){.internal-link target=_blank} section.

///

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

            if (outputFile.exists()) {
                outputFile.delete();
            }
        }
    }

    // Test variable replacement logic without triggering component dependencies
    public void test_variable_replacement_logic() throws Exception {
        // Test the variable replacement logic directly
        final List<String> commands =

# Settings and Environment Variables { #settings-and-environment-variables }

In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.

Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.

For this reason it's common to provide them in environment variables that are read by the application.

/// tip

                double variance = (maxTime - minTime) / avgTime;
                // JVM timing in concurrent scenarios is inherently variable
                // We verify implementation correctness rather than precise timing
                assertTrue(variance < 50.0,
                        String.format(