from typing import Optional

from fastapi import FastAPI
from pydantic import BaseModel


class Item(BaseModel):
    name: str
    description: Optional[str] = None


app = FastAPI()


@app.post("/items/")
def create_item(item: Item):
    return item


@app.get("/items/")
def read_items() -> list[Item]:
    return [
        Item(
            name="Portal Gun",

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *

    assertTrue("Expected another permutation, but there was none.", permutations.hasNext());
    assertEquals(expectedPermutation, permutations.next());
  }

  private <T> void assertNoMorePermutations(Iterator<List<T>> permutations) {
    assertFalse("Expected no more permutations, but there was one.", permutations.hasNext());
    try {
      permutations.next();

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()

쿼리 매개변수를 선언할 때와 같이, 모델 어트리뷰트가 기본 값을 가지고 있어도 이는 필수가 아닙니다. 그외에는 필수입니다. 그저 `None`을 사용하여 선택적으로 만들 수 있습니다.

예를 들면, 위의 이 모델은 JSON "`object`" (혹은 파이썬 `dict`)을 다음과 같이 선언합니다:

```JSON
{
    "name": "Foo",
    "description": "선택적인 설명란",
    "price": 45.2,
    "tax": 3.5
}
```

...`description`과 `tax`는 (기본 값이 `None`으로 되어 있어) 선택적이기 때문에, 이 JSON "`object`"는 다음과 같은 상황에서도 유효합니다:

```JSON
{
    "name": "Foo",

So we have a dedicated thread for every socket that just reads frames and dispatches them.

The reader thread must never run application-layer code. Otherwise one slow stream can hold up the entire connection.

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *

    void testInitDefaultsSetsAllFields() throws CIFSException {
        BaseConfiguration testConfig = new BaseConfiguration(false);
        testConfig.initDefaults();

        // Check random and time zone
        assertNotNull(testConfig.getRandom());
        assertNotNull(testConfig.getLocalTimezone());

        // Check PID is set
        assertTrue(testConfig.getPid() >= 0);

print(f"Hello {name} from Python")
```

/// tip

第二个参数是 <a href="https://docs.python.org/zh-cn/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> 的默认返回值。

如果没有提供，默认值为 `None`，这里我们提供 `"World"` 作为默认值。

///

然后你可以调用这个 Python 程序：

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console
// 这里我们还没有设置环境变量
$ python main.py

// 因为我们没有设置环境变量，所以我们得到的是默认值