When building web APIs with FastAPI, if there's an error in our code, FastAPI will normally contain it to the single request that triggered the error. 🛡

The client will get a **500 Internal Server Error** for that request, but the application will continue working for the next requests instead of just crashing completely.

### Bigger Errors - Crashes

Downloading and installing the package dependencies **could take minutes**, but using the **cache** would **take seconds** at most.

And as you would be building the container image again and again during development to check that your code changes are working, there's a lot of accumulated time this would save.

<font color="#4E9A06">INFO</font>:     Application startup complete.
```

</div>

In the output, there's a line with something like:

```hl_lines="4"
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

That line shows the URL where your app is being served, in your local machine.

### Check it

message PodSchedulingContext {
  // Standard object metadata
  // +optional
  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;

  // Spec describes where resources for the Pod are needed.
  optional PodSchedulingContextSpec spec = 2;

  // Status describes where resources for the Pod can be allocated.
  // +optional
  optional PodSchedulingContextStatus status = 3;
}

            //
            // TODO: This seems a little indirect. Is there a better way to do this? For FE1.0 there is
            // a special `TypeAliasConstructorDescriptor` for this case. For FIR there is
            // FirConstructor.originalConstructorIfTypeAlias but that doesn't seem to help here as it
            // is null for the constructors we get.

* It will **limit and filter** the output data to what is defined in the return type.
    * This is particularly important for **security**, we'll see more of that below.

## `response_model` Parameter

There are some cases where you need or want to return some data that is not exactly what the type declares.

In Python 3.10 there's also a **new syntax** where you can put the possible types separated by a <abbr title='also called "bitwise or operator", but that meaning is not relevant here'>vertical bar (`|`)</abbr>.

=== "Python 3.10+"

    ```Python hl_lines="1"
    {!> ../../../docs_src/python_types/tutorial008b_py310.py!}

Use the `./gradlew :architecture-test:sortAcceptedApiChanges` task to sort the file.

4. Validate your changes before committing.\
Run the `./gradlew sanityCheck` task again to make sure there are no more errors.

#### Filtering changes by severity

There is a somewhat non-obvious filter present on the page that allows you to control which type of messages are displayed.

## OpenAPI Client Generators

There are many tools to generate clients from **OpenAPI**.

A common tool is <a href="https://openapi-generator.tech/" class="external-link" target="_blank">OpenAPI Generator</a>.

					}
				}
			}

			// Wait for the tick, if the there exist a local endpoint in discovery.
			// Non docker/kubernetes environment we do not need to wait.
			if !foundLocal && orchestrated {
				<-keepAliveTicker.C
			}
		}
	}

	// On Kubernetes/Docker setups DNS resolves inappropriately sometimes
	// where there are situations same endpoints with multiple disks