return False
  if not whitelist_prefix:
    return True

  for prefix in whitelist_prefix:
    if var_name.startswith(prefix):
      return True
  return False


def main(parsed_args: argparse.Namespace):
  converted_vars = {}

  for var, value in os.environ.items():
    if not value or not should_convert(var,
                                       parsed_args.blacklist,

# Advanced User Guide { #advanced-user-guide }

## Additional Features { #additional-features }

The main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} should be enough to give you a tour through all the main features of **FastAPI**.

In the next sections you will see other options, configurations, and additional features.

/// tip

The next sections are **not necessarily "advanced"**.

## Call `uvicorn` { #call-uvicorn }

In your FastAPI application, import and run `uvicorn` directly:

{* ../../docs_src/debugging/tutorial001.py hl[1,15] *}

### About `__name__ == "__main__"` { #about-name-main }

The main purpose of the `__name__ == "__main__"` is to have some code that is executed when your file is called with:

<div class="termy">

```console
$ python myapp.py
```

</div>

.nav-link>.fab,.main-header.text-sm .nav-link>.fad,.main-header.text-sm .nav-link>.fal,.main-header.text-sm .nav-link>.far,.main-header.text-sm .nav-link>.fas,.main-header.text-sm .nav-link>.ion,.main-header.text-sm .nav-link>.svg-inline--fa,.text-sm .main-header .nav-link>.fa,.text-sm .main-header .nav-link>.fab,.text-sm .main-header .nav-link>.fad,.text-sm .main-header .nav-link>.fal,.text-sm .main-header .nav-link>.far,.text-sm .main-header .nav-link>.fas,.text-sm .main-header .nav-link>.ion,.text-sm...

Para rodar qualquer um dos exemplos, copie o codigo para um arquivo `main.py`, e inicie o `uvivorn` com:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:solid">main.py</u>

  <span style="background-color:#009485"><font color="#D3D7CF"> FastAPI </font></span>  Starting development server 🚀

   <span style="background-color:#007166"><font color="#D3D7CF"> module </font></span>  🐍 main.py

     <span style="background-color:#007166"><font color="#D3D7CF"> code </font></span>  Importing the FastAPI app object from the module with the
             following code:

{* ../../docs_src/first_steps/tutorial001.py *}

Copia eso en un archivo `main.py`.

Ejecuta el servidor en vivo:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:single">main.py</u>
<font color="#3465A4">INFO    </font> Using path <font color="#3465A4">main.py</font>

然後你可以呼叫這個 Python 程式：

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

<div class="termy">

```console
// 這裡我們還沒有設定環境變數
$ python main.py

// 因為我們沒有設定環境變數，所以我們得到的是預設值

Hello World from Python

// 但是如果我們事先建立過一個環境變數
$ export MY_NAME="Wade Wilson"

// 然後再次呼叫程式
$ python main.py

// 現在就可以讀取到環境變數了

Hello Wade Wilson from Python
```

</div>

////

//// tab | Windows PowerShell

## How it looks { #how-it-looks }

Let's first just use the code and see how it works, and then we'll come back to understand what's happening.

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

Copy the example in a file `main.py`:

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

## Run it { #run-it }

/// info

  /**
   * Returns an exception handler that exits the system. This is particularly useful for the main
   * thread, which may start up other, non-daemon threads, but fail to fully initialize the
   * application successfully.
   *
   * <p>Example usage:
   *
   * <pre>
   * public static void main(String[] args) {
   *   Thread.currentThread().setUncaughtExceptionHandler(UncaughtExceptionHandlers.systemExit());
   *   ...