is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, in HTTP Basic

                available, instead of erroring out, the dependency result will be
                `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, in a query
                parameter or in an HTTP Bearer token).

                is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, with OpenID
                Connect or in a cookie).

                is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, with OAuth2
                or in a cookie).

Environment variables could be useful for handling application **settings**, as part of the **installation** of Python, etc.

## Create and Use Env Vars { #create-and-use-env-vars }

Most of these ideas would be more or less **independent**, and in most cases you should only need to study them if they apply directly to **your project**.

If something seems interesting and useful to your project, go ahead and check it, but otherwise, you might probably just skip them.

/// tip

## Raw Data { #raw-data }

If you need to send data **without** JSON encoding, use `raw_data` instead of `data`.

This is useful for sending pre-formatted text, log lines, or special <dfn title="A value used to indicate a special condition or state">"sentinel"</dfn> values like `[DONE]`.

{* ../../docs_src/server_sent_events/tutorial003_py310.py hl[17] *}

And then, that system (in this case **FastAPI**) will take care of doing whatever is needed to provide your code with those needed dependencies ("inject" the dependencies).

This is very useful when you need to:

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

    return spec.toCacheBuilder().lenientParsing();
  }

  /**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   * This is especially useful for command-line configuration of a {@code CacheBuilder}.
   *
   * @param spec a String in the format specified by {@link CacheBuilderSpec}
   * @since 12.0
   */
  @GwtIncompatible // To be supported

/// note

`jsonable_encoder` is actually used by **FastAPI** internally to convert data. But it is useful in many other scenarios.