# Dependencies { #dependencies }

**FastAPI** has a very powerful but intuitive **<abbr title="also known as components, resources, providers, services, injectables">Dependency Injection</abbr>** system.

It is designed to be very simple to use, and to make it very easy for any developer to integrate other components with **FastAPI**.

## What is "Dependency Injection" { #what-is-dependency-injection }

* vSphere cloud provider: Remove the dependency of login information on worker nodes for vsphere cloud provider. ([#43545](https://github.com/kubernetes/kubernetes/pull/43545), [@luomiao](https://github.com/luomiao))

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import org.mockito.ArgumentCaptor;
import org.mockito.Mock;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.junit.jupiter.MockitoExtension;

import jcifs.CIFSException;

import org.junit.jupiter.api.Nested;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import org.mockito.ArgumentCaptor;
import org.mockito.junit.jupiter.MockitoExtension;

import jcifs.CIFSContext;
import jcifs.Configuration;
import jcifs.SmbConstants;

import java.util.Map;
import org.jspecify.annotations.Nullable;

/**
 * A {@link CharEscaper} that uses an array to quickly look up replacement characters for a given
 * {@code char} value. An additional safe range is provided that determines whether {@code char}
 * values without specific replacements are to be considered safe and left unescaped or should be
 * escaped in a general way.
 *

	ErrMalformedBucketObjectConfig = errors.New("invalid bucket object lock config")
	// ErrInvalidRetentionDate - indicates that retention date needs to be in ISO 8601 format
	ErrInvalidRetentionDate = errors.New("date must be provided in ISO 8601 format")
	// ErrPastObjectLockRetainDate - indicates that retention date must be in the future
	ErrPastObjectLockRetainDate = errors.New("the retain until date must be in the future")

Having `str | None` will allow your editor to give you better support and detect errors.

///

## Additional validation { #additional-validation }

We are going to enforce that even though `q` is optional, whenever it is provided, **its length doesn't exceed 50 characters**.

### Import `Query` and `Annotated` { #import-query-and-annotated }

To achieve that, first import:

* `Query` from `fastapi`
* `Annotated` from `typing`

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package lifecycle

import (
	"encoding/xml"
	"time"
)

var (
	errLifecycleInvalidDate         = Errorf("Date must be provided in ISO 8601 format")
	errLifecycleInvalidDays         = Errorf("Days must be positive integer when used with Expiration")

import org.junit.jupiter.api.Nested;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import org.mockito.ArgumentCaptor;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;

import jcifs.CIFSContext;
import jcifs.dcerpc.DcerpcHandle;

```

/// tip

The second argument to <a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> is the default value to return.

If not provided, it's `None` by default, here we provide `"World"` as the default value to use.

///

Then you could call that Python program:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console