能举个重构的例子吗

当然可以。假设你有一个函数，叫做"计算订单总价"，它现在只支持一种商品和一种折扣。

def calculate_total(price, quantity, discount):
    return price * quantity * (1 - discount)

一开始没问题，但后来加了会员折扣、满减、运费等，代码变成了这样：

def calculate_total(price, quantity, discount, member_discount, free_shipping_threshold, shipping_fee):
    total = price * quantity * (1 - discount)
    if total > 100:  # 满100减20
        total -= 20
    total = total * (1 - member_discount)
    if total < free_shipping_threshold:
        total += shipping_fee
    return total

这个函数现在参数很多，逻辑混杂，很难看懂和修改。

重构的思路：把不同计算逻辑拆成独立的小函数，并让主函数只负责组合它们。

重构后：

def calculate_subtotal(price, quantity):
    return price * quantity

def apply_coupon_discount(amount, discount):
    return amount * (1 - discount)

def apply_full_reduction(amount):
    if amount > 100:
        return amount - 20
    return amount

def apply_member_discount(amount, member_discount):
    return amount * (1 - member_discount)

def add_shipping(amount, free_shipping_threshold, shipping_fee):
    if amount < free_shipping_threshold:
        return amount + shipping_fee
    return amount

def calculate_total(price, quantity, discount, member_discount, free_shipping_threshold, shipping_fee):
    subtotal = calculate_subtotal(price, quantity)
    after_coupon = apply_coupon_discount(subtotal, discount)
    after_reduction = apply_full_reduction(after_coupon)
    after_member = apply_member_discount(after_reduction, member_discount)
    total = add_shipping(after_member, free_shipping_threshold, shipping_fee)
    return total

这样，每个小函数只做一件事，名字也说明了它做什么。如果以后修改折扣规则，只需改apply_coupon_discount，不会影响其他逻辑。这就是一个典型的例子：提取函数的重构。