Python内置模块enum枚举类型的创建使用小结_Python

一、开篇：告别"魔术数字"

你的代码里有多少这样的"魔术数字"？

# ❌ 魔术数字——三个月后谁都看不懂
if status == 1:
    print("处理中")
elif status == 2:
    print("已完成")
elif status == 0:
    print("已取消")

# ✅ 枚举——意图一目了然
from enum import enum

class orderstatus(enum):
    cancelled = 0
    processing = 1
    completed = 2

if status == orderstatus.processing:
    print("处理中")

💡 枚举（enum）给一组相关的常量赋予有意义的名字。它提高代码可读性、防止拼写错误、约束取值范围——是消除"魔术数字"的利器。

二、基本使用

2.1 创建和访问枚举

from enum import enum

class color(enum):
    red = 1
    green = 2
    blue = 3

# 三种访问方式
print(color.red)          # color.red
print(color["red"])       # color.red  —— 通过名字
print(color(1))           # color.red  —— 通过值

# 枚举成员的属性
print(color.red.name)     # "red"   —— 名字
print(color.red.value)    # 1       —— 值

# 比较
print(color.red == color.red)    # true
print(color.red == color.blue)   # false
print(color.red is color.red)    # true —— 同一成员是单例
# print(color.red > color.green)  # typeerror —— 不支持大小比较（除非intenum）

# 迭代
for color in color:
    print(f"  {color.name} = {color.value}")

2.2 auto()自动赋值

from enum import enum, auto

class status(enum):
    pending = auto()     # 1
    approved = auto()    # 2
    rejected = auto()    # 3
    cancelled = auto()   # 4

print([(s.name, s.value) for s in status])
# [('pending', 1), ('approved', 2), ('rejected', 3), ('cancelled', 4)]

# 自定义auto行为
class myauto(enum):
    def _generate_next_value_(name, start, count, last_values):
        """自定义auto生成的value"""
        return name.lower()  # 用名字的小写作为值

class configkey(myauto):
    host = auto()      # "host"
    port = auto()      # "port"
    debug = auto()     # "debug"

print([(k.name, k.value) for k in configkey])

三、枚举的变体

3.1 intenum——可与整数比较

from enum import intenum

class priority(intenum):
    low = 1
    medium = 3
    high = 5
    urgent = 10

# intenum可以当作整数使用
print(priority.high == 5)       # true
print(priority.high > priority.low)  # true  —— 支持大小比较
print(priority.high + 1)        # 6

# 但和普通enum相比，失去了类型安全性
# priority.high == 5是true——可能不是你想要的

3.2 flag——位标志

from enum import flag, auto

class permission(flag):
    none = 0
    read = auto()      # 1
    write = auto()     # 2
    delete = auto()    # 4
    admin = read | write | delete  # 7

# 组合权限
user_perms = permission.read | permission.write  # 3
print(user_perms)                          # permission.read|write
print(permission.read in user_perms)       # true
print(permission.delete in user_perms)     # false

# 赋予权限
user_perms |= permission.delete
print(permission.admin in user_perms)      # true

# 实战：文件权限系统
def can_access(required, user_permission):
    """检查用户是否有足够的权限"""
    return required in user_permission

print(can_access(permission.read, permission.read | permission.write))  # true
print(can_access(permission.delete, permission.read | permission.write)) # false

四、实战案例

4.1 api状态码

from enum import intenum

class httpstatus(intenum):
    """http状态码枚举"""
    ok = 200
    created = 201
    bad_request = 400
    unauthorized = 401
    forbidden = 403
    not_found = 404
    internal_error = 500

    def is_success(self):
        return 200 <= self.value < 300

    def is_client_error(self):
        return 400 <= self.value < 500

def handle_response(status_code, body):
    """处理http响应"""
    status = httpstatus(status_code)
    if status.is_success():
        print(f"✓ {status.name}: {body}")
    elif status.is_client_error():
        print(f"✗ {status.name}: 客户端错误")
    else:
        print(f"⚠ {status.name}: 服务器错误")

handle_response(200, "操作成功")
handle_response(404, none)

4.2 配置选项

from enum import enum

class loglevel(enum):
    debug = 10
    info = 20
    warning = 30
    error = 40

    def __ge__(self, other):
        """支持 >= 比较"""
        if self.__class__ is other.__class__:
            return self.value >= other.value
        return notimplemented

class logconfig:
    current_level = loglevel.info

    @classmethod
    def set_level(cls, level):
        if not isinstance(level, loglevel):
            raise typeerror(f"请使用loglevel枚举，而不是 {type(level)}")
        cls.current_level = level

    @classmethod
    def should_log(cls, level):
        return level >= cls.current_level

# 使用——类型安全，不会传错
logconfig.set_level(loglevel.debug)
print(logconfig.should_log(loglevel.info))  # true

五、总结

枚举让一组相关的常量有了类型和名字。它是消除"魔术数字"和提高代码可读性的标准方式。

💡 选型指南：

类型	用途	特点
enum	通用枚举	类型安全，不可与整型混用
intenum	兼容整数的枚举	可与整数比较、运算
flag	位标志	支持位运算组合
auto()	自动赋值	不关心具体值时使用