We are going to start from where we left in the previous chapter and increment it.

## About JWT { #about-jwt }

JWT means "JSON Web Tokens".

It's a standard to codify a JSON object in a long dense string without spaces. It looks like this:

```
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
```

 * Second, it is always backed by an array large enough to hold a value for every possible
 * combination of row and column keys. (This is rarely optimal unless the table is extremely dense.)
 * Finally, every possible combination of row and column keys is always considered to have a value
 * associated with it: It is not possible to "remove" a value, only to replace it with {@code null},

    *   Added `sparse_gradient` option (default=false) that makes the gradient of these functions/ops sparse (`IndexedSlices`) instead of dense (`Tensor`), using new `SparseSegmentSum/Mean/SqrtNGradV2` ops.

*   `tf.nn.embedding_lookup_sparse`

    *   Optimized this function for some cases by fusing internal operations.

*   `tf.saved_model.SaveOptions`

    }

    /**
     * Throws {@link UnsupportedOperationException}. This method is inherited from {@link
     * ImmutableMap.Builder}, but it does not make sense for bimaps.
     *
     * @throws UnsupportedOperationException always
     * @deprecated This method does not make sense for bimaps and should not be called.
     * @since 31.1
     */
    @DoNotCall
    @Deprecated
    @Override

...Although if the whole application is just **crashing immediately** it probably doesn't make sense to keep restarting it forever. But in those cases, you will probably notice it during development, or at least right after deployment.

So let's focus on the main cases, where it could crash entirely in some particular cases **in the future**, and it still makes sense to restart it.

///

If you have a big application, you might end up accumulating **several tags**, and you would want to make sure you always use the **same tag** for related *path operations*.

In these cases, it could make sense to store the tags in an `Enum`.

**FastAPI** supports that the same way as with plain strings:

{* ../../docs_src/path_operation_configuration/tutorial002b.py hl[1,8:10,13,18] *}

They work the same way as for other FastAPI endpoints/*path operations*:

{* ../../docs_src/websockets/tutorial002_an_py310.py hl[68:69,82] *}

/// info

As this is a WebSocket it doesn't really make sense to raise an `HTTPException`, instead we raise a `WebSocketException`.

### Burger Conclusion { #burger-conclusion }

In this scenario of "fast food burgers with your crush", as there is a lot of waiting 🕙, it makes a lot more sense to have a concurrent system ⏸🔀⏯.

This is the case for most of the web applications.

Many, many users, but your server is waiting 🕙 for their not-so-good connection to send their requests.

            try {
                return send0(loc, request, response, params);
            } catch (final SmbException smbe) {
                // Retrying only makes sense if the invalid parameter is an tree id. If we have a stale file descriptor
                // retrying make no sense, as it will never become available again.
                if (params.contains(RequestParam.NO_RETRY)

"_Si vous cherchez à apprendre un **framework moderne** pour créer des APIs REST, regardez **FastAPI** [...] C'est rapide, facile à utiliser et à apprendre [...]_"

"_Nous sommes passés à **FastAPI** pour nos **APIs** [...] Je pense que vous l'aimerez [...]_"