变量改名

变量改名（Rename Variable）给一个变量换一个说明它用途的名字。它解决的痛是：读代码的人要先推断 tmp、data、a 里装的是什么，推错了就写出错的代码。

一个场景

一个销售报表函数，统计已付款订单的总额和各城市的金额。当初写得快，三个变量叫 a、tmp、data。

前后对比

"""销售报表：改名前。"""

import json


def report(orders: list[dict]) -> tuple[float, dict[str, float]]:
    a = [o for o in orders if o["paid"]]
    tmp = sum(o["amount"] for o in a)
    data: dict[str, float] = {}
    for o in a:
        data[o["city"]] = data.get(o["city"], 0.0) + o["amount"]
    return tmp, data


ORDERS = [
    {"city": "北京", "amount": 200.0, "paid": True},
    {"city": "上海", "amount": 100.0, "paid": True},
    {"city": "北京", "amount": 50.0, "paid": False},
]

if __name__ == "__main__":
    print(json.dumps(report(ORDERS), ensure_ascii=False))

# 输出：
# [300.0, {"北京": 200.0, "上海": 100.0}]

// 销售报表：改名前。
interface Order {
  city: string;
  amount: number;
  paid: boolean;
}

export function report(orders: Order[]): [number, Record<string, number>] {
  const a = orders.filter((o) => o.paid);
  const tmp = a.reduce((s, o) => s + o.amount, 0);
  const data: Record<string, number> = {};
  for (const o of a) {
    data[o.city] = (data[o.city] ?? 0) + o.amount;
  }
  return [tmp, data];
}

const ORDERS: Order[] = [
  { city: "北京", amount: 200, paid: true },
  { city: "上海", amount: 100, paid: true },
  { city: "北京", amount: 50, paid: false },
];

console.log(JSON.stringify(report(ORDERS)));

// 输出：
// [300,{"北京":200,"上海":100}]

"""销售报表：改名后。"""

import json


def report(orders: list[dict]) -> tuple[float, dict[str, float]]:
    paid_orders = [order for order in orders if order["paid"]]
    paid_total = sum(order["amount"] for order in paid_orders)
    total_by_city: dict[str, float] = {}
    for order in paid_orders:
        total_by_city[order["city"]] = total_by_city.get(order["city"], 0.0) + order["amount"]
    return paid_total, total_by_city


ORDERS = [
    {"city": "北京", "amount": 200.0, "paid": True},
    {"city": "上海", "amount": 100.0, "paid": True},
    {"city": "北京", "amount": 50.0, "paid": False},
]

if __name__ == "__main__":
    print(json.dumps(report(ORDERS), ensure_ascii=False))

# 输出：
# [300.0, {"北京": 200.0, "上海": 100.0}]

// 销售报表：改名后。
interface Order {
  city: string;
  amount: number;
  paid: boolean;
}

export function report(orders: Order[]): [number, Record<string, number>] {
  const paidOrders = orders.filter((order) => order.paid);
  const paidTotal = paidOrders.reduce((sum, order) => sum + order.amount, 0);
  const totalByCity: Record<string, number> = {};
  for (const order of paidOrders) {
    totalByCity[order.city] = (totalByCity[order.city] ?? 0) + order.amount;
  }
  return [paidTotal, totalByCity];
}

const ORDERS: Order[] = [
  { city: "北京", amount: 200, paid: true },
  { city: "上海", amount: 100, paid: true },
  { city: "北京", amount: 50, paid: false },
];

console.log(JSON.stringify(report(ORDERS)));

// 输出：
// [300,{"北京":200,"上海":100}]

改名之后，不看函数名也能从变量名读出这个函数在做什么：筛出已付款的订单，算总额，按城市分。data 改成 total_by_city 之后，还顺带说明了字典的键是城市、值是金额。

定义与适用场景

变量改名：把变量的名字改成能说明它用途的名字，并改掉所有引用它的地方。变量的作用域越大，名字越重要：函数里用三行就结束的循环变量叫 i 无妨，贯穿整个函数的变量叫 tmp 就会让每个读者都停下来猜。改名用 IDE 的 Rename 命令，它只改引用，不会误改字符串或注释里碰巧相同的文字（IDE 可自动完成）。改的是常量或模块级变量时，Rename 会一并改掉别的文件里的引用。

什么时候别用

短小的匿名函数和两三行的循环里，x、i 这种名字是惯例，改成长名字反而显得啰嗦。名字也不是越长越好，paid_orders 比 list_of_orders_that_have_been_paid 好。