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枚举类

时间:2019-06-06 14:10:10      阅读:103      评论:0      收藏:0      [点我收藏+]

当需要定义常量时,一个办法是用大写变量通过整数来定义
好处是简单,缺点是类型是int,并且仍然是变量
Enum可以把一组相关常量定义在一个class中,且class不可变,而且成员可以直接比较,这样这些相关常量就不会变化了

 

  使用枚举类

    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)   #value属性则是自动赋给成员的int常量,默认从1开始计数
        
    #输出:Jan => Month.Jan , 1
    #输出:Feb => Month.Feb , 2
    #输出:Mar => Month.Mar , 3
    #输出:Apr => Month.Apr , 4
    #输出:May => Month.May , 5
    #输出:Jun => Month.Jun , 6
    #输出:Jul => Month.Jul , 7
    #输出:Aug => Month.Aug , 8
    #输出:Sep => Month.Sep , 9
    #输出:Oct => Month.Oct , 10
    #输出:Nov => Month.Nov , 11
    #输出:Dec => Month.Dec , 12

 

  自定义枚举类

  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    #@unique装饰器可以帮助我们检查保证没有重复值
    class Weekday(Enum):
        Sun = 00
        Mon = 01
        Tue = 02
        Wed = 03
        Thu = 04
        Fri = 05
        Sat = 06
        
    day1 = Weekday.Mon
    print(day1)    #输出:Weekday.Mon
    print(day1.value)    #输出:01,value属性是枚举常量的值
    
    print(Weekday.Tue)  #输出:Weekday.Tue
    print(Weekday[Tue])  #输出:Weekday.Tue,可用成员名称引用枚举常量
    print(Weekday[Tue].value)  #输出:02
    
    print(day1 == Weekday.Mon)  #输出:True
    print(day1 == Weekday.Tue)  #输出:False
    
    print(Weekday(03))    #输出:Weekday.Wed,根据value值获取枚举常量
    print(Weekday(03).value)    #输出:03,根据value值获取枚举常量
    
    print(day1 == Weekday(01))   #输出:True
    Weekday(7)    #报错
    
    for name, member in Weekday.__members__.items():
        print(name, =>, member)

    #输出:Sun => Weekday.Sun
    #输出:Mon => Weekday.Mon
    #输出:Tue => Weekday.Tue
    #输出:Wed => Weekday.Wed
    #输出:Thu => Weekday.Thu
    #输出:Fri => Weekday.Fri
    #输出:Sat => Weekday.Sat

 

枚举类

原文:https://www.cnblogs.com/shiliye/p/10984520.html

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