# Bigger Applications - Multiple Files

If you are building an application or a web API, it's rarely the case that you can put everything in a single file.

**FastAPI** provides a convenience tool to structure your application while keeping all the flexibility.

/// info

If you come from Flask, this would be the equivalent of Flask's Blueprints.

///

## An example file structure

Let's say you have a file structure like this:

```

## Other Return Type Annotations

There might be cases where you return something that is not a valid Pydantic field and you annotate it in the function, only to get the support provided by tooling (the editor, mypy, etc).

### Return a Response Directly

  // A vector to keep track of newly created `tf::Tensor` objects.
  std::vector<Tensor> all_input_tensors;
  // Update the vector with information from `input_tensors` if provided.
  if (input_tensors != nullptr) {
    // Note that we take the address of the elements in `all_input_tensors`
    // below. Allocate enough space so that no reallocation happens, which will
    // make the pointers invalid.

Porque nós podemos confiar nele para receber o `username` e o `password`, pois nós controlamos isso.

Mas se nós estamos construindo uma aplicação OAuth2 que outros poderiam conectar (i.e., se você está construindo um provedor de autenticação equivalente ao Facebook, Google, GitHub, etc.) você deveria utilizar um dos outros fluxos.

O mais comum é o fluxo implícito.

/// info

Even after OpenAPI 3.1.0 was released with this new simpler integration with JSON Schema, for a while, Swagger UI, the tool that provides the automatic docs, didn't support OpenAPI 3.1.0 (it does since version 5.0.0 🎉).

Because of that, versions of FastAPI previous to 0.99.0 still used versions of OpenAPI lower than 3.1.0.

///

### Dependency Injection

FastAPI incluye un sistema de <abbr title='En español: Inyección de Dependencias. También conocido en inglés cómo: "components", "resources", "services", "providers"'><strong>Dependency Injection</strong></abbr> extremadamente poderoso y fácil de usar.

* Inclusive las dependencias pueden tener dependencias creando una jerarquía o un **"grafo" de dependencias**.

	sendLog(ctx, entry)
}

// ErrCritical is the value panic'd whenever CriticalIf is called.
var ErrCritical struct{}

// CriticalIf logs the provided error on the console. It fails the
// current go-routine by causing a `panic(ErrCritical)`.
func CriticalIf(ctx context.Context, err error, errKind ...interface{}) {
	if err != nil {
		LogIf(ctx, "", err, errKind...)

	iamConfigPolicyDBGroupsPrefix          = iamConfigPolicyDBPrefix + "groups/"

	// IAM identity file which captures identity credentials.
	iamIdentityFile = "identity.json"

	// IAM policy file which provides policies for each users.
	iamPolicyFile = "policy.json"

	// IAM group members file
	iamGroupMembersFile = "members.json"

	// IAM format file
	iamFormatFile = "format.json"

	iamFormatVersion1 = 1

	}

	return nil
}

// Maximum running concurrent saves on server.
var maxConcurrentScannerSaves = make(chan struct{}, 4)

// save the content of the cache to minioMetaBackgroundOpsBucket with the provided name.
// Note that no locking is done when saving.
func (d *dataUsageCache) save(ctx context.Context, store objectIO, name string) error {
	select {
	case <-ctx.Done():
		return ctx.Err()

message ValidatingAdmissionPolicySpec {
  // ParamKind specifies the kind of resources used to parameterize this policy.
  // If absent, there are no parameters for this policy and the param CEL variable will not be provided to validation expressions.
  // If ParamKind refers to a non-existent kind, this policy definition is mis-configured and the FailurePolicy is applied.