# 獲取北京的人口
print(cities["北京"]["population"])  # 輸出: 21893095

# 獲取上海的第一個(gè)地標(biāo)
print(cities["上海"]["landmarks"][0])  # 輸出: 外灘

# 錯(cuò)誤示例：嘗試訪問(wèn)不存在的"廣州"
print(cities["廣州"]["population"])  # KeyError: '廣州'

# 安全獲取廣州人口（不存在則返回None）
guangzhou_pop = cities.get("廣州", {}).get("population")
print(guangzhou_pop)  # 輸出: None

# 帶默認(rèn)值的鏈?zhǔn)皆L問(wèn)
shanghai_landmarks = cities.get("上海", {}).get("landmarks", [])
print(shanghai_landmarks[0])  # 輸出: 外灘

# 更新上海的人口
cities["上海"]["population"] = 25000000
print(cities["上海"]["population"])  # 輸出: 25000000

# 添加新城市
cities["廣州"] = {
    "population": 18676605,
    "area_km2": 7434.4,
    "landmarks": ["小蠻腰", "陳家祠"]
}

# 錯(cuò)誤！cities中沒(méi)有"深圳"，無(wú)法直接操作其子鍵
cities["深圳"]["population"] = 17560000  # KeyError

# 安全創(chuàng)建新城市
if "深圳" not in cities:
    cities["深圳"] = {}  # 先創(chuàng)建空子字典
cities["深圳"]["population"] = 17560000

permissions = {
    "admin": {
        "dashboard": ["read", "write", "delete"],
        "users": ["read", "write"]
    },
    "editor": {
        "dashboard": ["read", "write"],
        "users": ["read"]
    }
}

# 檢查admin是否有users的delete權(quán)限
has_delete = "delete" in permissions.get("admin", {}).get("users", [])
print(has_delete)  # 輸出: False

students = {
    "張三": [85, 90, 78],  # 數(shù)學(xué)、英語(yǔ)、物理成績(jī)
    "李四": [92, 88, 95]
}

# 獲取張三的第一門(mén)成績(jī)
print(students["張三"][0])  # 輸出: 85

# 添加李四的新成績(jī)
students["李四"].append(82)
print(students["李四"])  # 輸出: [92, 88, 95, 82]

# 修改張三的第二門(mén)成績(jī)
students["張三"][1] = 95

# 計(jì)算所有學(xué)生的平均分
averages = {
    name: sum(scores) / len(scores) 
    for name, scores in students.items()
}
print(averages)  # 輸出: {'張三': 87.666..., '李四': 91.75}

# 找出平均分高于90的學(xué)生
top_students = [name for name, avg in averages.items() if avg > 90]
print(top_students)  # 輸出: ['李四']

products = {
    "iPhone 15": [
        {"color": "黑色", "storage": "128GB", "stock": 50},
        {"color": "白色", "storage": "256GB", "stock": 30}
    ],
    "MacBook Air": [
        {"color": "銀色", "storage": "256GB", "stock": 20}
    ]
}

# 查詢iPhone 15的黑色128GB庫(kù)存
for variant in products["iPhone 15"]:
    if variant["color"] == "黑色" and variant["storage"] == "128GB":
        print(variant["stock"])  # 輸出: 50

# 安全添加新SKU
if "iPhone 15" in products:
    products["iPhone 15"].append({"color": "藍(lán)色", "storage": "512GB", "stock": 15})

user_profile = {
    "id": 1001,
    "username": "python_lover",
    "profile": {  # 嵌套字典
        "bio": "Python愛(ài)好者",
        "location": "杭州"
    },
    "posts": [  # 嵌套列表
        {
            "id": 201,
            "content": "今天學(xué)習(xí)了字典嵌套！",
            "likes": 42,
            "comments": [  # 列表中嵌套字典
                {"user": "coder1", "text": "太有用了！"},
                {"user": "data_guy", "text": "收藏了"}
            ]
        },
        {
            "id": 202,
            "content": "Mermaid圖表真酷",
            "likes": 28
        }
    ]
}

# 獲取第一條post的第一個(gè)評(píng)論內(nèi)容
first_comment = (
    user_profile.get("posts", [{}])[0]  # 獲取posts列表，取第一個(gè)元素（或空字典）
    .get("comments", [{}])[0]           # 獲取comments列表，取第一個(gè)元素
    .get("text", "無(wú)評(píng)論")              # 獲取text
)
print(first_comment)  # 輸出: 太有用了！

# 錯(cuò)誤示范：直接索引可能崩潰
# print(user_profile["posts"][0]["comments"][0]["text"]) 

def safe_get(data, *keys, default=None):
    """安全獲取嵌套數(shù)據(jù)"""
    for key in keys:
        if isinstance(data, dict):
            data = data.get(key, default)
        elif isinstance(data, list) and isinstance(key, int):
            data = data[key] if key < len(data) else default
        else:
            return default
        if data is default:
            break
    return data

# 用法示例
bio = safe_get(user_profile, "profile", "bio")
print(bio)  # 輸出: Python愛(ài)好者

comment = safe_get(user_profile, "posts", 0, "comments", 0, "text")
print(comment)  # 輸出: 太有用了！

import requests

# 獲取北京天氣（示例API，實(shí)際使用需替換有效key）
response = requests.get("https://api.openweathermap.org/data/2.5/weather?q=Beijing&appid=YOUR_API_KEY")
data = response.json()  # 返回嵌套字典

# 提取關(guān)鍵信息
temperature = data["main"]["temp"] - 273.15  # 開(kāi)爾文轉(zhuǎn)攝氏度
humidity = data["main"]["humidity"]
wind_speed = data["wind"]["speed"]

print(f"北京溫度: {temperature:.1f}°C, 濕度: {humidity}%, 風(fēng)速: {wind_speed} m/s")

# 錯(cuò)誤代碼
print(user_profile["posts"][2]["content"])  # posts只有2個(gè)元素，索引2越界

# 安全訪問(wèn)第3條post
post = user_profile["posts"][2] if len(user_profile["posts"]) > 2 else None
if post:
    print(post["content"])

# 錯(cuò)誤：把列表當(dāng)字典用
print(user_profile["posts"]["comments"])  # posts是列表，不能用字符串索引