一文带你了解Python枚举类enum的使用
目录
- 简介
- 初试
- 遍历
- 可哈希
- 访问成员
- 唯一枚举值
- 自动枚举值
- 比较运算
- 功能性API
- IntEnum
- IntFlag
- Flag
简介
枚举是与多个唯一常量绑定的一组符号
因为枚举表示的是常量,建议枚举成员名用大写
IntEnum 便于进行系统交互
初试
from enum import Enum class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 print(Color.RED) # Color.RED print(repr(Color.RED)) # <Color.RED: 1> print(type(Color.RED)) # <enum 'Color'> print(isinstance(Color.GREEN, Color)) # True print(Color.RED.name) # RED
遍历
from enum import Enum class Shake(Enum): VANILLA = 7 CHOCOLATE = 4 COOKIES = 9 MINT = 3 for shake in Shake: print(shake) # Shake.VANILLA # Shake.CHOCOLATE # Shake.COOKIES # Shake.MINT
__members__ 列出 name 和成员
from enum import Enum class Shape(Enum): SQUARE = 2 DIAMOND = 1 CIRCLE = 3 ALIAS_FOR_SQUARE = 2 for name, member in Shape.__members__.items(): print(name, member) # SQUARE Shape.SQUARE # DIAMOND Shape.DIAMOND # CIRCLE Shape.CIRCLE # ALIAS_FOR_SQUARE Shape.SQUARE
可哈希
枚举成员可哈希,可用于字典和集合
from enum import Enum class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 apples = {} apples[Color.RED] = 'red delicious' apples[Color.GREEN] = 'granny smith' print(apples) # {<Color.RED: 1>: 'red delicious', <Color.GREEN: 2>: 'granny smith'}
访问成员
- name:变量名
- value:值
from enum import Enum class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 # 通过值访问 print(Color(1)) # Color.RED print(Color(3)) # Color.BLUE # 通过name访问 print(Color['RED']) # Color.RED print(Color['GREEN']) # Color.GREEN # 访问成员的name或value print(Color.RED.name) # RED print(Color.RED.value) # 1
唯一枚举值
装饰器 @unique
from enum import Enum, unique @unique class Mistake(Enum): ONE = 1 TWO = 2 THREE = 3 FOUR = 3 # ValueError: duplicate values found in <enum 'Mistake'>: FOUR -> THREE
自动枚举值
如果枚举值不重要,可以用 auto(), 默认从 1 开始
from enum import Enum, auto class Color(Enum): RED = auto() BLUE = auto() GREEN = auto() print(Color(1)) # Color.RED print(list(Color)) # [<Color.RED: 1>, <Color.BLUE: 2>, <Color.GREEN: 3>]
比较运算
- Enum 不支持直接排序
- IntEnum 可直接排序
Enum
from enum import Enum class Color(Enum): RED = 1 BLUE = 2 GREEN = 3 print(Color.RED is Color.RED) # True print(Color.RED is Color.BLUE) # False print(Color.RED is not Color.BLUE) # True try: Color.RED < Color.BLUE # Enum不支持直接排序 except Exception as e: print(e) # '<' not supported between instances of 'Color' and 'Color' print(Color.BLUE == Color.RED) # Fasle print(Color.BLUE != Color.RED) # True print(Color.BLUE == Color.BLUE) # True print(Color.BLUE == 2) # False
IntEnum
from enum import IntEnum class Color(IntEnum): RED = 1 BLUE = 2 GREEN = 3 # IntEnum可直接排序 print(Color.RED < Color.BLUE) # True print(Color.BLUE == 2) # True
功能性API
from enum import Enum class Animal(Enum): ANT = 1 BEE = 2 CAT = 3 DOG = 4 Animal = Enum('Animal', 'ANT BEE CAT DOG') # 同上 print(Animal) # <enum 'Animal'> print(Animal.ANT) # <Animal.ANT: 1> print(Animal.ANT.value) # 1 print(list(Animal)) # [<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]
IntEnum
除了不可以直接和 Enum 比较,其他都类似整数
from enum import Enum, IntEnum class Color(Enum): RED = 1 GREEN = 2 class Shape(IntEnum): CIRCLE = 1 SQUARE = 2 class Request(IntEnum): POST = 1 GET = 2 print(Shape.CIRCLE == Color.RED) # False print(Shape == 1) # False print(Shape.CIRCLE == 1) # True print(Shape.CIRCLE == Request.POST) # True print(int(Shape.CIRCLE)) # 1 print(['a', 'b', 'c'][Shape.CIRCLE]) # b print([i for i in range(Shape.SQUARE)]) # [0, 1]
IntFlag
类似 int,IntFlag 成员使用按位运算符得到的结果仍然是 IntFlag 成员
IntFlag 和 Enum 的一个区别在于,如果没有设置任何标志(值为 0),则其布尔值为 False
from enum import IntFlag class Perm(IntFlag): R = 4 # 读 W = 2 # 写 X = 1 # 执行 print(Perm.R | Perm.W) # <Perm.R|W: 6> print(Perm.R + Perm.W) # 6 RW = Perm.R | Perm.W print(Perm.R in RW) # True
from enum import IntFlag class Perm(IntFlag): R = 4 # 读 W = 2 # 写 X = 1 # 执行 RWX = 7 # 读写执行 print(Perm.RWX) # <Perm.RWX: 7> print(~Perm.RWX) # <Perm.-8: -8> print(Perm.R & Perm.X) # <Perm.0: 0> print(bool(Perm.R & Perm.X)) # False print(Perm.X | 8) # <Perm.8|X: 9>
Flag
- Flag 与 IntFlag 类似,成员可使用按位运算符进行组合,但不可与其他 Flag 或 int 组合
- 推荐用 auto() 作为值
from enum import Flag, auto class Color(Flag): BLACK = 0 RED = auto() BLUE = auto() GREEN = auto() WHITE = RED | BLUE | GREEN print(Color.RED & Color.GREEN) # <Color.0: 0> print(bool(Color.RED & Color.GREEN)) # False print(Color.WHITE) # <Color.WHITE: 7> print(Color.BLACK) # <Color.BLACK: 0> print(bool(Color.BLACK)) # False
知识点
不支持同名
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