Strategy 模式

from abc import ABC, abstractmethod
from typing import Protocol


class DiscountStrategy(Protocol):
    """折扣策略接口"""

    def calculate_discount(self, price: float) -> float:
        ...


class NoDiscount:
    """无折扣策略"""

    def calculate_discount(self, price: float) -> float:
        return 0.0


class PercentageDiscount:
    """百分比折扣策略"""

    def __init__(self, percentage: float):
        self.percentage = percentage

    def calculate_discount(self, price: float) -> float:
        return price * self.percentage / 100


class FixedAmountDiscount:
    """固定金额折扣策略"""

    def __init__(self, amount: float):
        self.amount = amount

    def calculate_discount(self, price: float) -> float:
        return min(self.amount, price)


class SeasonalDiscount:
    """季节性折扣策略"""

    def calculate_discount(self, price: float) -> float:
        # 假设当前季节有8折优惠
        return price * 0.2


class ShoppingCart:
    """购物车上下文"""

    def __init__(self, strategy: DiscountStrategy):
        self.strategy = strategy
        self.items: list[tuple[str, float]] = []

    def add_item(self, item: str, price: float) -> None:
        self.items.append((item, price))

    def set_discount_strategy(self, strategy: DiscountStrategy) -> None:
        self.strategy = strategy

    def calculate_total(self) -> float:
        subtotal = sum(price for _, price in self.items)
        discount = self.strategy.calculate_discount(subtotal)
        return subtotal - discount

    def print_receipt(self) -> None:
        total = self.calculate_total()
        print(f"=== 购物小票 ===")
        for item, price in self.items:
            print(f"{item}: ¥{price}")
        print(f"总计: ¥{total:.2f}")


# 使用
def main():
    # 创建购物车
    cart = ShoppingCart(NoDiscount())
    cart.add_item("Python编程书", 89)
    cart.add_item("机械键盘", 299)

    # 无折扣
    print("无折扣:")
    cart.print_receipt()

    # 百分比折扣
    cart.set_discount_strategy(PercentageDiscount(15))
    print("\n85折优惠:")
    cart.print_receipt()

    # 固定金额折扣
    cart.set_discount_strategy(FixedAmountDiscount(50))
    print("\n立减50元:")
    cart.print_receipt()


if __name__ == "__main__":
    main()

import zlib
import gzip
import json
from abc import ABC, abstractmethod
from typing import Protocol


class CompressionStrategy(Protocol):
    """压缩策略接口"""

    def compress(self, data: str) -> bytes:
        ...

    def decompress(self, data: bytes) -> str:
        ...


class NoCompression:
    """无压缩策略"""

    def compress(self, data: str) -> bytes:
        return data.encode('utf-8')

    def decompress(self, data: bytes) -> str:
        return data.decode('utf-8')


class ZlibCompression:
    """Zlib 压缩策略"""

    def compress(self, data: str) -> bytes:
        return zlib.compress(data.encode('utf-8'))

    def decompress(self, data: bytes) -> str:
        return zlib.decompress(data).decode('utf-8')


class GzipCompression:
    """Gzip 压缩策略"""

    def compress(self, data: str) -> bytes:
        return gzip.compress(data.encode('utf-8'))

    def decompress(self, data: bytes) -> str:
        return gzip.decompress(data).decode('utf-8')


class JSONCompression:
    """JSON 格式化压缩策略"""

    def compress(self, data: str) -> bytes:
        # 先解析为JSON，再压缩
        obj = json.loads(data)
        return gzip.compress(json.dumps(obj).encode('utf-8'))

    def decompress(self, data: bytes) -> str:
        return gzip.decompress(data).decode('utf-8')


class DataProcessor:
    """数据处理器上下文"""

    def __init__(self, strategy: CompressionStrategy):
        self.strategy = strategy

    def set_strategy(self, strategy: CompressionStrategy) -> None:
        self.strategy = strategy

    def save_data(self, data: str, filename: str) -> None:
        """保存数据（应用压缩）"""
        compressed = self.strategy.compress(data)
        with open(filename, 'wb') as f:
            f.write(compressed)
        print(f"数据已保存到 {filename}")

    def load_data(self, filename: str) -> str:
        """加载数据（应用解压）"""
        with open(filename, 'rb') as f:
            compressed = f.read()
        return self.strategy.decompress(compressed)


# 使用
def main():
    # 准备数据
    data = json.dumps({"name": "Alice", "age": 30, "city": "Beijing"})

    processor = DataProcessor(NoCompression())
    processor.save_data("data_plain.txt", data)

    # 使用 Zlib 压缩
    processor.set_strategy(ZlibCompression())
    processor.save_data("data_zlib.bin", data)
    print(f"解压: {processor.load_data('data_zlib.bin')}")

    # 使用 Gzip 压缩
    processor.set_strategy(GzipCompression())
    processor.save_data("data_gzip.bin", data)
    print(f"解压: {processor.load_data('data_gzip.bin')}")


if __name__ == "__main__":
    main()