* `dict`의 키(key)는 `str`타입이다. (각 아이템의 이름(name))
    * `dict`의 값(value)는 `float`타입이다. (각 아이템의 가격(price))

#### `Optional`

`str`과 같이 타입을 선언할 때 `Optional`을 쓸 수도 있는데, "선택적(Optional)"이기때문에 `None`도 될 수 있습니다:

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

`Optional[str]`을 `str` 대신 쓰게 되면, 특정 값이 실제로는 `None`이 될 수도 있는데 항상 `str`이라고 가정하는 상황에서 에디터가 에러를 찾게 도와줄 수 있습니다.

#### Generic(제네릭) 타입

import org.codelibs.fess.mylasta.action.FessMessages;
import org.codelibs.fess.mylasta.action.FessUserBean;
import org.codelibs.fess.mylasta.direction.FessConfig;
import org.dbflute.hook.AccessContext;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.core.message.MessageManager;
import org.lastaflute.core.time.TimeManager;
import org.lastaflute.db.dbflute.accesscontext.AccessContextArranger;
import org.lastaflute.web.TypicalAction;

import org.lastaflute.web.validation.Required;

/**
 * Form for uploading files to the storage system via the admin API.
 * This form is used in the admin API interface to upload files to the storage backend
 * with optional path specification for file organization.
 */
public class UploadForm {

    /**
     * The storage path where the file should be uploaded.
     * If not specified, the file will be stored in the default location.

import org.codelibs.fess.app.web.base.FessSearchAction;
import org.codelibs.fess.app.web.login.LoginAction;
import org.codelibs.fess.mylasta.action.FessUserBean;
import org.codelibs.fess.util.ComponentUtil;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.HtmlResponse;

/**
 * The logout action.
 */
public class LogoutAction extends FessSearchAction {

    /**

import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.List;
import java.util.Set;

/**
 * Optional features of classes derived from {@code List}.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible

import com.google.common.collect.testing.features.TesterAnnotation;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.Set;

/**
 * Optional features of classes derived from {@link Multiset}.
 *
 * @author Louis Wasserman
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible

 *
 */
public interface BeanConfigurationValuePreprocessor {

    /**
     * Preprocesses the specified bean configuration value. The optional type provided to this method is a hint (not a
     * requirement) for the preprocessor to resolve the value to a compatible value or a (string) value than can be

* Créer un répertoire `app` et y entrer.
* Créez un fichier `main.py` avec :

```Python
from typing import Optional

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Optional[str] = None):
    return {"item_id": item_id, "q": q}
```

        return artifact.isSelectedVersionKnown();
    }

    /** {@inheritDoc} */
    @Override
    public void setOptional(boolean optional) {
        artifact.setOptional(optional);
    }

    /** {@inheritDoc} */
    @Override
    public int hashCode() {
        int result = 17;

        result = 37 * result + getGroupId().hashCode();

import org.codelibs.fess.opensearch.config.exentity.FileConfig;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;