python基础——枚举类

时间：2023-03-09 15:31:03
python基础——枚举类

python基础——枚举类

　　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'))

　　这样我们就获得了Month类型的枚举类，可以直接使用Month.Jan来引用一个常量，或者枚举它的所有成员：

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。

　　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

　　@unique装饰器可以帮助我们检查保证没有重复值。

　　访问这些枚举类型可以有若干种方法：

>>> day1 = Weekday.Mon

>>> print(day1)

Weekday.Mon

>>> print(Weekday.Tue)

Weekday.Tue

>>> print(Weekday['Tue'])

Weekday.Tue

>>> print(Weekday.Tue.value)

2

>>> print(day1 == Weekday.Mon)

True

>>> print(day1 == Weekday.Tue)

False

>>> print(Weekday(1))

Weekday.Mon

>>> print(day1 == Weekday(1))

True

>>> Weekday(7)

Traceback (most recent call last):

  ...

ValueError: 7 is not a valid Weekday

>>> for name, member in Weekday.__members__.items():

...     print(name, '=>', member)

...

Sun => Weekday.Sun

Mon => Weekday.Mon

Tue => Weekday.Tue

Wed => Weekday.Wed

Thu => Weekday.Thu

Fri => Weekday.Fri

Sat => Weekday.Sat

　　可见，既可以用成员名称引用枚举常量，又可以直接根据value的值获得枚举常量。

小结

　　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。

参考源码：

#python 枚举类   示例

#2016-8-30 18:55:25

#MengmengCoding

# -*- coding: utf-8 -*-

from enum import Enum

#Enum是一个枚举类

#Month,Weekday各为一个Enum类的实例化

Month=Enum('Month',('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'))

Weekday=Enum('Weekday',('Mon','Tue','Wed','Thu','Fri','Sat','Sun'))

for name,member in Month.__members__.items():

    print(name,'=>',member,',',member.value)

print('--------cut-off line--------')

#输出：

'''

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

'''

for name,member in Weekday.__members__.items():

    print(name,'=>',member,',',member.value)

print('--------cut-off line--------')

#输出：

'''

Mon => Weekday.Mon , 1

Tue => Weekday.Tue , 2

Wed => Weekday.Wed , 3

Thu => Weekday.Thu , 4

Fri => Weekday.Fri , 5

Sat => Weekday.Sat , 6

Sun => Weekday.Sun , 7

'''

#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

#这里还是用周来举例吧，谁让我见识少呢~

#用WeekDay来区别之前的Weekday吧 

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):    #由Enum类派生得到

    Sun=0

    Mon=1

    Tue=2

    Wed=3

    Thu=4

    Fri=5

    Sat=6

day1=WeekDay.Mon 

print('day1=',day1)

print('WeekDay.Tue=',WeekDay.Tue)

print('WeekDay[\'Tue\']=',WeekDay['Tue'])

print('WeekDay.Tue.value=',WeekDay.Tue.value)

print('day1==WeekDay.Mon ?',day1==WeekDay.Mon)

print('day1==WeekDay.Tue ?',day1==WeekDay.Tue)

print('day1==WeekDay(1) ?',day1==WeekDay(1))

#输出：

'''

day1= WeekDay.Mon

WeekDay.Tue= WeekDay.Tue

WeekDay['Tue']= WeekDay.Tue

WeekDay.Tue.value= 2

day1==WeekDay.Mon ? True

day1==WeekDay.Tue ? False

day1==WeekDay(1) ? True

'''

print('--------cut-off line--------')

for name,member in WeekDay.__members__.items():

    print(name,'=>',member)

#输出：

'''

Sun => WeekDay.Sun

Mon => WeekDay.Mon

Tue => WeekDay.Tue

Wed => WeekDay.Wed

Thu => WeekDay.Thu

Fri => WeekDay.Fri

Sat => WeekDay.Sat

'''

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