## 선택적 매개변수

같은 방법으로 기본값을 `None`으로 설정하여 선택적 매개변수를 선언할 수 있습니다:

```Python hl_lines="9"
{!../../docs_src/query_params/tutorial002.py!}
```

이 경우 함수 매개변수 `q`는 선택적이며 기본값으로 `None` 값이 됩니다.

/// check | "확인"

**FastAPI**는 `item_id`가 경로 매개변수이고 `q`는 경로 매개변수가 아닌 쿼리 매개변수라는 것을 알 정도로 충분히 똑똑합니다.

///

/// note | "참고"

FastAPI는 `q`가 `= None`이므로 선택적이라는 것을 인지합니다.

		debug.PrintStack()
		return metacache{}
	}

	// Grab a write lock, since we create one if we cannot find one.
	b.mu.Lock()
	defer b.mu.Unlock()

	// Check if exists already.
	if c, ok := b.caches[o.ID]; ok {
		c.lastHandout = time.Now()
		b.caches[o.ID] = c
		b.debugf("returning existing %v", o.ID)
		return c
	}

	if !o.Create {
		return metacache{

   * @return the escaped form of {@code string}
   * @throws NullPointerException if {@code string} is null
   */
  @Override
  public String escape(String string) {
    checkNotNull(string); // GWT specific check (do not optimize)
    // Inlineable fast-path loop which hands off to escapeSlow() only if needed
    int length = string.length();
    for (int index = 0; index < length; index++) {

```Python hl_lines="21"
{!../../docs_src/path_operation_configuration/tutorial005.py!}
```

/// info | "情報"

`respnse_description`は具体的にレスポンスを参照し、`description`は*path operation*全般を参照していることに注意してください。

///

/// check | "確認"

OpenAPIは*path operation*ごとにレスポンスの説明を必要としています。

そのため、それを提供しない場合は、**FastAPI** が自動的に「成功のレスポンス」を生成します。

///

<img src="https://fastapi.tiangolo.com/img/tutorial/path-operation-configuration/image03.png">

import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.ToIntFunction;
import java.util.stream.Collector;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link SortedMultiset} whose contents will never change, with many other important properties
 * detailed at {@link ImmutableCollection}.
 *

		vc, err = globalBucketVersioningSys.Get(bucket)
		if err != nil {
			return err
		}

		// Check if the current bucket has a configured lifecycle policy
		lc, err = globalLifecycleSys.Get(bucket)
		if err != nil && !errors.Is(err, BucketLifecycleNotFound{Bucket: bucket}) {
			return err
		}

		// Check if bucket is object locked.
		lr, err = globalBucketObjectLockSys.Get(bucket)
		if err != nil {
			return err

     * removed in one segment while checking another, in which case the table was never actually
     * empty at any point. (The sum ensures accuracy up through at least 1<<31 per-segment
     * modifications before recheck.)  Method containsValue() uses similar constructions for
     * stability checks.
     */
    long sum = 0L;
    Segment<K, V, E, S>[] segments = this.segments;

    // Check the user response. It has the application's original request.
    cacheMiss.assertCode(200)
      .assertBody("B")
      .assertHeader("Donut", "b")
      .assertRequestUrl(server.url("/"))
      .assertSentRequestAtMillis(request2SentAt, request2ReceivedAt)
      .assertReceivedResponseAtMillis(request2SentAt, request2ReceivedAt)

       * No code ever sees this bogus value for `endpoint`: This class overrides both methods that
       * use the `endpoint` field, compareTo() and endpoint(). Additionally, the main implementation
       * of Cut.compareTo checks for belowAll before reading accessing `endpoint` on another Cut
       * instance.
       */
      super("");
    }

    @Override
    Comparable<?> endpoint() {

 * `java.net.URL` it's possible to create an awkward URL like `http:/` with scheme and path but no
 * hostname. Building APIs that consume such malformed values is difficult!
 *
 * This class has a modern API. It avoids punitive checked exceptions: [toHttpUrl] throws
 * [IllegalArgumentException] on invalid input or [toHttpUrlOrNull] returns null if the input is an
 * invalid URL. You can even be explicit about whether each component has been encoded already.
 *