字典特點：

• 使用鍵值對(key-value pairs)儲存數據
• 鍵(key)必須是唯一的
• 鍵必須是不可變類型（字符串、數字、元組）
• 值(value)可以是任何類型
• 字典是可變的（mutable）

# 創建字典
empty_dict = {}
empty_dict2 = dict()

# 基本字典
student = {
    "name": "張三",
    "age": 20,
    "score": 85
}

# 使用dict()函數創建
info = dict(name="李四", age=22, city="台北")

# 混合數據類型
mixed = {
    1: "整數鍵",
    "list": [1, 2, 3],
    "tuple": (4, 5, 6),
    "dict": {"a": 1, "b": 2}
}

# 訪問值
student = {"name": "張三", "age": 20, "score": 85}
print(student["name"])  # 張三
print(student.get("age"))  # 20
print(student.get("phone", "未設置"))  # 使用默認值

# 修改值
student["age"] = 21
student["phone"] = "123456789"  # 添加新鍵值對
student.update({"email": "zhang@example.com", "age": 22})

# 刪除鍵值對
del student["phone"]
email = student.pop("email")
last_item = student.popitem()  # 刪除並返回最後一個鍵值對

學生成績管理系統

class_scores = {
    "張三": {"數學": 85, "英語": 92, "物理": 78},
    "李四": {"數學": 92, "英語": 85, "物理": 90},
    "王五": {"數學": 78, "英語": 85, "物理": 95}
}

# 計算每個學生的平均分
for student, scores in class_scores.items():
    average = sum(scores.values()) / len(scores)
    print(f"{student}的平均分是：{average:.1f}")

購物車系統

shopping_cart = {}

def add_item(item, price, quantity=1):
    if item in shopping_cart:
        shopping_cart[item]["quantity"] += quantity
    else:
        shopping_cart[item] = {"price": price, "quantity": quantity}

def calculate_total():
    return sum(item["price"] * item["quantity"] for item in shopping_cart.values())

add_item("蘋果", 30, 2)
add_item("香蕉", 25, 3)
add_item("蘋果", 30, 1)  # 增加已有商品的數量

print(f"購物車總金額：{calculate_total()}元")

# 字典推導式
squares = {x: x**2 for x in range(5)}  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# 合併字典
dict1 = {"a": 1, "b": 2}
dict2 = {"c": 3, "d": 4}
merged = {**dict1, **dict2}  # Python 3.5+

# 遍歷字典
student = {"name": "張三", "age": 20, "score": 85}
for key in student.keys():
    print(key)
for value in student.values():
    print(value)
for key, value in student.items():
    print(f"{key}: {value}")