```

这表示 `item` 可以是 `int` 或 `str`。

#### 可能为 `None` { #possibly-none }

你可以声明一个值的类型是某种类型（比如 `str`），但它也可能是 `None`。

//// tab | Python 3.10+

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

////

使用 `str | None` 而不是仅仅 `str`，可以让编辑器帮助你发现把值当成总是 `str` 的错误（实际上它也可能是 `None`）。

### 类作为类型 { #classes-as-types }

你也可以把类声明为变量的类型。

          else -> {
            CipherSuite.forJavaName(cipherSuiteString)
          }
        }

      val tlsVersionString = checkNotNull(protocol) { "tlsVersion == null" }
      if ("NONE" == tlsVersionString) throw IOException("tlsVersion == NONE")
      val tlsVersion = TlsVersion.forJavaName(tlsVersionString)

      val peerCertificatesCopy =
        try {
          peerCertificates.toImmutableList()

    if not (config.site_url or "").endswith(f"{lang}/") and lang != "en":
        config.site_url = f"{config.site_url}{lang}/"
    return config


def resolve_file(*, item: str, files: Files, config: MkDocsConfig) -> None:
    item_path = Path(config.docs_dir) / item
    if not item_path.is_file():
        en_src_dir = (Path(config.docs_dir) / "../../en/docs").resolve()
        potential_path = en_src_dir / item

import subprocess

from playwright.sync_api import Playwright, sync_playwright


# Run playwright codegen to generate the code below, copy paste the sections in run()
def run(playwright: Playwright) -> None:
    browser = playwright.chromium.launch(headless=False)
    # Update the viewport manually
    context = browser.new_context(viewport={"width": 960, "height": 1080})
    page = context.new_page()
    page.goto("http://localhost:8000/docs")

## therefore we run master _AFTER_ we run 6.8 which uses an earlier gradle version
export JAVA_HOME="${HOME}"/.java/${ES_BUILD_JAVA}

     *
     * @param namePrefix the prefix that JAR file names should start with
     * @return an array of File objects representing matching JAR files, or empty array if none found
     */
    public static File[] getJarFiles(final String namePrefix) {
        final ServletContext context = LaServletContextUtil.getServletContext();
        if (context == null) {
            return new File[0];

import subprocess
import time

import httpx
from playwright.sync_api import Playwright, sync_playwright


# Run playwright codegen to generate the code below, copy paste the sections in run()
def run(playwright: Playwright) -> None:
    browser = playwright.chromium.launch(headless=False)
    # Update the viewport manually
    context = browser.new_context(viewport={"width": 960, "height": 1080})
    page = context.new_page()

            DcerpcHandle handle = mock(DcerpcHandle.class);
            LsaPolicyHandle policy = mock(LsaPolicyHandle.class);
            jcifs.SID[] none = new jcifs.SID[0];

            cache.resolveSids(handle, policy, none);
            verify(handle, times(1)).sendrecv(any(jcifs.dcerpc.msrpc.MsrpcLookupSids.class));
        }
    }

import subprocess
import time

import httpx
from playwright.sync_api import Playwright, sync_playwright


# Run playwright codegen to generate the code below, copy paste the sections in run()
def run(playwright: Playwright) -> None:
    browser = playwright.chromium.launch(headless=False)
    # Update the viewport manually
    context = browser.new_context(viewport={"width": 960, "height": 1080})
    browser = playwright.chromium.launch(headless=False)

from collections.abc import AsyncIterable, Iterable

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None


items = [
    Item(name="Plumbus", description="A multi-purpose household device."),
    Item(name="Portal Gun", description="A portal opening device."),
    Item(name="Meeseeks Box", description="A box that summons a Meeseeks."),
]