You put it on top of a function. Like a pretty decorative hat (I guess that's where the term came from).

    A "decorator" takes the function below and does something with it.

    In our case, this decorator tells **FastAPI** that the function below corresponds to the **path** `/` with an **operation** `get`.

    It is the "**path operation decorator**".

You can also use the other operations:

* `@app.post()`

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

## Documenting the callback

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

      - tutorial/dependencies/index.md
      - tutorial/dependencies/classes-as-dependencies.md
      - tutorial/dependencies/sub-dependencies.md
      - tutorial/dependencies/dependencies-in-path-operation-decorators.md
      - tutorial/dependencies/global-dependencies.md
      - tutorial/dependencies/dependencies-with-yield.md
    - Security:
      - tutorial/security/index.md
      - tutorial/security/first-steps.md

* **Extensible**:
    * Pydantic allows custom data types to be defined or you can extend validation with methods on a model decorated with the validator decorator.

import org.eclipse.aether.named.providers.NoopNamedLockFactory;
import org.eclipse.aether.spi.artifact.ArtifactPredicateFactory;
import org.eclipse.aether.spi.artifact.decorator.ArtifactDecoratorFactory;
import org.eclipse.aether.spi.artifact.generator.ArtifactGeneratorFactory;
import org.eclipse.aether.spi.checksums.ProvidedChecksumsSource;
import org.eclipse.aether.spi.checksums.TrustedChecksumsSource;

    * <a href="https://fastapi.tiangolo.com/tutorial/dependencies/dependencies-in-path-operation-decorators/" class="external-link" target="_blank">Tutorial - Dependencies - Dependencies in path operation decorators</a>.
    * <a href="https://fastapi.tiangolo.com/tutorial/dependencies/global-dependencies/" class="external-link" target="_blank">Tutorial - Dependencies - Global Dependencies</a>.

```Python
def get_settings():
    return Settings()
```

we would create that object for each request, and we would be reading the `.env` file for each request. ⚠️

But as we are using the `@lru_cache` decorator on top, the `Settings` object will be created only once, the first time it's called. ✔️

=== "Python 3.9+"

    ```Python hl_lines="1  11"
    {!> ../../../docs_src/settings/app03_an_py39/main.py!}
    ```

    * Add experimental supports conversion of models that may be larger than 2GB before buffer deduplication

### Bug Fixes and Other Changes

* `tf.py_function` and `tf.numpy_function` can now be used as function decorators for clearer code:
   ```
   @tf.py_function(Tout=tf.float32)
   def my_fun(x):
     print("This always executes eagerly.")
     return x+1
   ```

* `tf.lite`