python面向對象和面向過程的區別，Python實用筆記 （27）面向對象高級編程——使用枚舉類

枚舉類型定義一個class類型，然后，每個常量都是class的一個唯一實例。Python提供了Enum類來實現這個功能：

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

這樣我們就獲得了Month類型的枚舉類，可以直接使用Month.Jan來引用一個常量，或者枚舉它的所有成員：

for name, member in Month.__members__.items():print(name, '=>', member, ',', member.value)

python面向對象和面向過程的區別、value屬性則是自動賦給成員的int常量，默認從1開始計數。

如果需要更精確地控制枚舉類型，可以從Enum派生出自定義類：

from enum import Enum, unique@unique
class Weekday(Enum): Sun = 0 # Sun的value被設定為0 Mon = 1 Tue = 2 Wed = 3 Thu = 4 Fri = 5 Sat = 6 

@unique裝飾器可以幫助我們檢查保證沒有重復值。

python枚舉法例子，訪問這些枚舉類型可以有若干種方法：

>>> 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 

可見，既可以用成員名稱引用枚舉常量，又可以直接根據value的值獲得枚舉常量。