from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list[str] | None, Query()] = None):
    query_items = {"q": q}

from typing import Union

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(
    strange_header: Union[str, None] = Header(default=None, convert_underscores=False),
):

<SelectObjectContentRequest>
    <Expression>SELECT * from s3object AS s</Expression>
    <ExpressionType>SQL</ExpressionType>
    <InputSerialization>
        <CompressionType>NONE</CompressionType>
        <CSV>
        <FileHeaderInfo>NONE</FileHeaderInfo>
	    <QuoteCharacter>"</QuoteCharacter>
        </CSV>
    </InputSerialization>
    <OutputSerialization>
        <JSON>
        </JSON>

 */
@Experimental
@Immutable
public enum DependencyScope {

    /**
     * None. Allows you to declare dependencies (for example to alter reactor build order) but in reality dependencies
     * in this scope are not part of any path scope.
     */
    NONE("none", false),

    /**
     * Undefined. When no scope is explicitly given, UNDEFINED will be used, but its meaning will depend on

                </mxCell>
                <mxCell id="3" value="&lt;font style=&quot;font-size: 24px&quot; face=&quot;Roboto&quot;&gt;Package app&lt;br&gt;app/__init__.py&lt;/font&gt;" style="text;html=1;strokeColor=none;fillColor=none;align=center;verticalAlign=middle;whiteSpace=wrap;rounded=0;strokeWidth=3;fontFamily=Roboto Mono, mono;FType=g;" parent="1" vertex="1">
                    <mxGeometry x="635" y="310" width="300" height="80" as="geometry"/>

from fastapi.testclient import TestClient
from pydantic.dataclasses import dataclass

app = FastAPI()


@dataclass
class Item:
    name: str
    price: Optional[float] = None
    owner_ids: Optional[List[int]] = None


@app.get("/items/invalid", response_model=Item)
def get_invalid():
    return {"name": "invalid", "price": "foo"}


@app.get("/items/innerinvalid", response_model=Item)

 *
 */
@Deprecated
public final class ArtifactStatus implements Comparable<ArtifactStatus> {
    /**
     * No trust - no information about status.
     */
    public static final ArtifactStatus NONE = new ArtifactStatus("none", 0);

    /**
     * No trust - information was generated with defaults.
     */
    public static final ArtifactStatus GENERATED = new ArtifactStatus("generated", 1);

    /**

from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

`Optional[Something]` là một cách viết ngắn gọn của `Union[Something, None]`, chúng là tương đương nhau.

Điều này cũng có nghĩa là trong Python 3.10, bạn có thể sử dụng `Something | None`:

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, min_length=3, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})