![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)

### Alternative API docs

And now, go to <a href="http://127.0.0.1:8000/redoc" class="external-link" target="_blank">http://127.0.0.1:8000/redoc</a>.

You will see the alternative automatic documentation (provided by <a href="https://github.com/Rebilly/ReDoc" class="external-link" target="_blank">ReDoc</a>):

    /**
     * 
     */
    public static final char[] HEX_DIGITS = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
    };


    /**
     * This is an alternative to the <code>java.lang.Integer.toHexString</code>
     * method. It is an efficient relative that also will pad the left side so
     * that the result is <code>size</code> digits.
     * 
     * @param val

![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)

### Alternative API docs

And now, go to <a href="http://127.0.0.1:8000/redoc" class="external-link" target="_blank">http://127.0.0.1:8000/redoc</a>.

You will see the alternative automatic documentation (provided by <a href="https://github.com/Rebilly/ReDoc" class="external-link" target="_blank">ReDoc</a>):

![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)

### Alternative API-Dokumentation

Gehen Sie jetzt auf <a href="http://127.0.0.1:8000/redoc" class="external-link" target="_blank">http://127.0.0.1:8000/redoc</a>.

Sie sehen die alternative automatische Dokumentation (bereitgestellt von <a href="https://github.com/Rebilly/ReDoc" class="external-link" target="_blank">ReDoc</a>):

        Cell a = as[i];
        if (a != null) sum += a.value;
      }
    }
    return sum;
  }

  /**
   * Resets variables maintaining the sum to zero. This method may be a useful alternative to
   * creating a new adder, but is only effective if there are no concurrent updates. Because this
   * method is intrinsically racy, it should only be used when it is known that no threads are
   * concurrently updating.

 * ExecutionException}, the exception's {@linkplain #getCause() cause} comes from a failed task,
 * possibly run in another thread.
 *
 * <p>{@code UncheckedExecutionException} is intended as an alternative to {@code
 * ExecutionException} when the exception thrown by a task is an unchecked exception. However, it
 * may also wrap a checked exception in some cases.
 *

        #### Utility: compare with alternatives


        There is always *some* alternative to adding a new feature to Guava, even if it's just
        forking Guava yourself.


        We want to see that new features have some significant advantage over the alternatives.
        These advantages can take

    "EEE, dd MMM yyyy HH:mm:ss zzz",
    // RFC 850, obsoleted by RFC 1036 with any TZ.
    "EEEE, dd-MMM-yy HH:mm:ss zzz",
    // ANSI C's asctime() format
    "EEE MMM d HH:mm:ss yyyy",
    // Alternative formats:
    "EEE, dd-MMM-yyyy HH:mm:ss z",
    "EEE, dd-MMM-yyyy HH-mm-ss z",
    "EEE, dd MMM yy HH:mm:ss z",
    "EEE dd-MMM-yyyy HH:mm:ss z",
    "EEE dd MMM yyyy HH:mm:ss z",
    "EEE dd-MMM-yyyy HH-mm-ss z",

# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

```

////

//// tab | Python 3.8+

```Python hl_lines="1  4"
{!> ../../docs_src/python_types/tutorial009.py!}
```

////

//// tab | Python 3.8+ Alternative

```Python hl_lines="1  4"
{!> ../../docs_src/python_types/tutorial009b.py!}
```

////

#### `Union` oder `Optional` verwenden?