# Exceptions - `HTTPException` and `WebSocketException`

These are the exceptions that you can raise to show errors to the client.

When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.

You can use:

* `HTTPException`
* `WebSocketException`

### Other utility functions { #other-utility-functions }

Any other utility function that you call directly can be created with normal `def` or `async def` and FastAPI won't affect the way you call it.

    assertData("827e") // 'e' == 4-byte follow-up length.
    assertData(format("%04X", payload.completeSegmentByteCount()))
    assertData(payload.readByteString())
  }

  @Test fun serverMessageLengthLong() {
    // Create a payload which will overflow the normal and short payload byte size.
    val payload = Buffer()
    while (payload.completeSegmentByteCount() <= PAYLOAD_SHORT_MAX) {

	margin-top: 0;
}

#result .title a:visited {
	color: #014c8c;
}

#result .body {
	display: flex;
	align-items: flex-start;
}

#result .site cite {
	color: #093;
	font-style: normal;
}

#result .more {
	display: none;
}

#result .info {
	font-size: 80%;
}

#result .url-copy {
	color: #007bff;
}

#result .url-copied {
	color: #2c974b;
}

* `datetime.date`:
    * Python `datetime.date`.
    * In requests and responses will be represented as a `str` in ISO 8601 format, like: `2008-09-15`.
* `datetime.time`:
    * A Python `datetime.time`.
    * In requests and responses will be represented as a `str` in ISO 8601 format, like: `14:23:55.003`.
* `datetime.timedelta`:

 *
 * <p>We can't use {@code PartiallyGwtIncompatible} because then the GWT compiler wouldn't recognize
 * it as a {@code GwtIncompatible} annotation. And for {@code Futures.catching}, we need the GWT
 * compiler to autostrip the normal server method in order to expose the special, inherited GWT
 * version.
 */
@GwtCompatible
final class Partially {
  /**
   * The presence of this annotation on an API indicates that the method <i>may</i> be used with the

Es solo una función estándar que puede recibir parámetros.

Puede ser una función `async def` o una función normal `def`, **FastAPI** sabrá cómo manejarla correctamente.

En este caso, la función de tarea escribirá en un archivo (simulando el envío de un email).

Y como la operación de escritura no usa `async` y `await`, definimos la función con un `def` normal:

{* ../../docs_src/background_tasks/tutorial001_py39.py hl[6:9] *}

		ACB_PWNOTREQ               = 0x00000004, /* 1 = User password not required */
		ACB_TEMPDUP                = 0x00000008, /* 1 = Temporary duplicate account */
		ACB_NORMAL                 = 0x00000010, /* 1 = Normal user account */
		ACB_MNS                    = 0x00000020, /* 1 = MNS logon user account */
		ACB_DOMTRUST               = 0x00000040, /* 1 = Interdomain trust account */

e,\"legendPosition\":\"right\",\"times\":[],\"addTimeMarker\":false,\"dimensions\":{\"x\":{\"accessor\":0,\"format\":{\"id\":\"date\",\"params\":{\"pattern\":\"HH:mm\"}},\"params\":{\"date\":true,\"interval\":\"PT10M\",\"format\":\"HH:mm\",\"bounds\":{\"min\":\"2019-07-28T10:40:08.271Z\",\"max\":\"2019-07-30T10:40:08.271Z\"}},\"aggType\":\"date_histogram\"},\"y\":[{\"accessor\":1,\"format\":{\"id\":\"number\"},\"params\":{},\"aggType\":\"count\"}]}},\"aggs\":[{\"id\":\"1\",\"enabled\":true,\"typ...

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001_py39.py hl[6:9] *}