类变量和实例变量的命名规范是什么？

在 Python 中，类变量和实例变量的命名没有强制的语法约束（不像关键字），但遵循PEP 8 规范和行业通用惯例能极大提升代码可读性，核心原则是「清晰区分变量归属、符合 Python 命名风格」。下面分两类变量讲透命名规范，包括核心规则、避坑点和最佳实践。

一、通用基础命名规范（适用于所有变量）

先明确 Python 变量命名的通用规则（类变量 / 实例变量均需遵守）：

1. 命名风格：全部使用小写字母，单词之间用下划线_分隔（蛇形命名法，snake_case），这是 PEP 8 对变量的核心要求；
2. 禁止使用：
   • 关键字（如class、def、self、if等）；
   • 单下划线开头 + 大写字母（如_ABC）（通常是模块内私有常量）；
   • 双下划线开头且结尾（如__init__）（Python 魔法方法 / 属性，保留字）；
3. 长度与语义：名称要体现变量的用途（见名知意），避免单字母（除了通用缩写，如i表示循环索引、x/y表示坐标）；
4. 禁止特殊字符：只能包含字母、数字、下划线，且不能以数字开头。

二、类变量的命名规范

类变量是「类的共享属性」，命名需突出「全局 / 共享 / 常量」的特性，核心规则如下：

示例：类变量命名

python

运行

class Student: # 常量类变量（全大写） MAX_SCORE = 100 DEFAULT_CLASS = "高一(1)班" # 普通共享类变量（蛇形命名） total_students = 0 pass_rate = 0.85 # 私有类变量（单下划线开头） _grade_mapping = {1: "一年级", 2: "二年级"} def __init__(self, name, score): self.name = name self.score = score # 修改类变量时遵循命名规范 Student.total_students += 1

类变量命名避坑点：

1. 不要用全小写命名常量类变量（如maxscore），无法区分 “可变共享变量” 和 “不可变常量”；
2. 不要用双下划线开头（如__total）：双下划线开头会触发 Python 的「名称改写（name mangling）」，变成_类名__变量名，仅用于 “类内私有” 的极端场景，非必要不要用；
3. 避免与实例变量同名：如类变量name和实例变量self.name同名，会导致实例访问时优先读实例变量，逻辑混乱（示例：class Student: name = "默认名"; def __init__(self, name): self.name = name）。

三、实例变量的命名规范

实例变量是「单个实例的独有属性」，命名需突出「实例专属 / 个体特征」，核心规则如下：

示例：实例变量命名

python

运行

class Order: # 类变量（常量） MAX_ITEMS = 20 def __init__(self, order_id, user_name, total_amount): # 普通实例变量 self.order_id = order_id self.user_name = user_name self.total_amount = total_amount self.items = [] # 私有实例变量（单下划线） self._payment_status = "unpaid" # 强私有实例变量（双下划线，慎用） self.__transaction_id = None def pay(self, trans_id): # 类内可访问私有实例变量 self._payment_status = "paid" self.__transaction_id = trans_id

实例变量命名避坑点：

1. 不要滥用双下划线：双下划线会增加代码复杂度（如子类无法直接访问、调试困难），仅当需要 “防止子类意外覆盖” 时使用；
2. 避免无意义命名：如self.x、self.data1，应改为self.coordinate_x、self.order_data；
3. 不要与内置属性 / 方法同名：如self.list、self.dict（应改为self.item_list、self.data_dict），避免覆盖内置类型。

四、命名规范总结（核心对照表）

五、最佳实践建议

1. 常量类变量必用全大写：如MAX_RETRY = 3，一眼能识别 “不可修改的类级常量”；
2. 实例变量优先单下划线私有：对外暴露的属性用普通命名，内部状态用单下划线（如self._status），符合 “最小暴露原则”；
3. 避免同名冲突：类变量和实例变量的名称尽量不重复，若必须重复（如特殊业务），需在注释中明确说明；
4. 团队统一规范：如果团队有自定义命名规则（如前缀cls_标识类变量），优先遵循团队规范（如cls_total_count），可读性优先于 “纯 PEP 8”。

遵循以上规范，既能符合 Python 官方标准，又能让其他开发者一眼区分 “类变量” 和 “实例变量”，大幅降低代码维护成本。

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