```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

`Optional[str]` ব্যবহার করা মানে হল শুধু `str` নয়, এটি হতে পারে `None`-ও, যা আপনার এডিটরকে সেই ত্রুটিগুলি শনাক্ত করতে সাহায্য করবে যেখানে আপনি ধরে নিচ্ছেন যে একটি মান সবসময় `str` হবে, অথচ এটি `None`-ও হতে পারেও।

@REM Apache Maven Upgrade Script
@REM
@REM Environment Variable Prerequisites
@REM
@REM   JAVA_HOME           (Optional) Points to a Java installation.
@REM   MAVEN_OPTS          (Optional) Java runtime options used when Maven is executed.
@REM   MAVEN_SKIP_RC       (Optional) Flag to disable loading of mavenrc files.
@REM -----------------------------------------------------------------------------

    /**
     * Creates a default toolchain instance using system defaults.
     *
     * @return Optional containing the default toolchain if available
     * @throws ToolchainFactoryException if default toolchain creation fails
     */
    @Nonnull
    Optional<Toolchain> createDefaultToolchain() throws ToolchainFactoryException;

 */
@Experimental
public interface ArtifactManager extends Service {

    /**
     * Returns the path of the file previously associated to this artifact
     * or {@code Optional.empty()} if no path has been associated.
     */
    @Nonnull
    Optional<Path> getPath(@Nonnull Artifact artifact);

    /**
     * Associates the given file path to the artifact.
     */
    void setPath(@Nonnull ProducedArtifact artifact, Path path);

    private static Optional<String> lookupMessage(int code) {
        int[] codes = WinError.WINERR_CODES;
        String[] msgs = WinError.WINERR_MESSAGES;
        for (int i = 0; i < codes.length; i++) {
            if (codes[i] == code) {
                return Optional.of(msgs[i]);
            }
        }
        return Optional.empty();
    }

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

Sử dụng `Optional[str]` thay cho `str` sẽ cho phép trình soạn thảo giúp bạn phát hiện các lỗi mà bạn có thể gặp như một giá trị luôn là một `str`, trong khi thực tế nó rất có thể là `None`.

    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }
        result += lengthIfKnown.get();
      }
      return Optional.of(result);
    }

    @Override

    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }
        result += lengthIfKnown.get();
      }
      return Optional.of(result);
    }

    @Override

```

////

#### Gebruik van `Union` of `Optional`

Als je een Python versie lager dan 3.10 gebruikt, is dit een tip vanuit mijn **subjectieve** standpunt:

* 🚨 Vermijd het gebruik van `Optional[EenType]`.
* Gebruik in plaats daarvan **`Union[EenType, None]`** ✨.

이 응용 프로그램을 예로 들어보겠습니다:

{* ../../docs_src/query_params_str_validations/tutorial001.py hl[9] *}

쿼리 매개변수 `q`는 `Optional[str]` 자료형입니다. 즉, `str` 자료형이지만 `None` 역시 될 수 있음을 뜻하고, 실제로 기본값은 `None`이기 때문에 FastAPI는 이 매개변수가 필수가 아니라는 것을 압니다.

/// note | 참고

FastAPI는 `q`의 기본값이 `= None`이기 때문에 필수가 아님을 압니다.

`Optional[str]`에 있는 `Optional`은 FastAPI가 사용하는게 아니지만, 편집기에게 더 나은 지원과 오류 탐지를 제공하게 해줍니다.

///

## 추가 검증