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目录
当我们需要定义常量时,一个办法是用大写变量通过整数来定义,例如月份:
- JAN = 1
- FEB = 2
- MAR = 3
- ...
- NOV = 11
- DEC = 12
好处是简单,缺点是类型是int
,并且仍然是变量。
更好的方法是为这样的枚举类型定义一个class类型,然后,每个常量都是class的一个唯一实例。Python提供了Enum
类来实现这个功能:
- from enum import Enum
- Month = Enum('Month', ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'))
- for name, member in Month.__members__.items():
- print(name, '=>', member, ',', member.value)
- Jan => Month.Jan , 1
- Feb => Month.Feb , 2
- Mar => Month.Mar , 3
- Apr => Month.Apr , 4
- May => Month.May , 5
- Jun => Month.Jun , 6
- Jul => Month.Jul , 7
- Aug => Month.Aug , 8
- Sep => Month.Sep , 9
- Oct => Month.Oct , 10
- Nov => Month.Nov , 11
- Dec => Month.Dec , 12
value
属性则是自动赋给成员的int
常量,默认从1
开始计数。
如果需要更精确地控制枚举类型,可以从Enum
派生出自定义类:
- from enum import Enum, unique
- @unique
- class Weekday(Enum):
- Sun = 0 # Sun的value被设定为0
- Mon = 1
- Tue = 2
- Wed = 3
- Thu = 4
- Fri = 5
- Sat = 6
- #调用枚举成员的 3 种方式
- >>>print(print(Weekday.Tue))
- Weekday.Tue
- >>>print(Weekday['Tue'])
- Weekday.Tue
- >>>print(Weekday(1))
- Weekday.Mon
-
- #调取枚举成员中的 value 和 name
- >>>print(Weekday.Mon.value)
- 1
- >>>print(Weekday.Mon.name)
- Mon
-
- #遍历枚举类中所有成员的2种方式
- >>> for name, member in Weekday.__members__.items():
- ... print(name, '=>', member)
- ...
- Sun => Weekday.Sun
- Mon => Weekday.Mon
- Tue => Weekday.Tue
- W

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