本篇主要介紹Python中枚舉類的用法，更多內容請參考:Python學習指南

當我們需要定義常量時，一個辦法就是用大寫變量通過整數來定義，例如月份：

JAN = 1
FEB = 2
MAR = 3
···
NOV = 11
DEC = 12

好處就是簡單，確定是類型是int，並且仍然是變量。

更好的辦法是為這樣的枚舉類型定義一個class類型，然後，每個常量都是class的一個唯一實例。Python提供了Enum來來實現這個功能：

from enum import Enum

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

這樣我們就獲得了Month類型的枚舉值，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)

value屬性則是自動賦給成員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：

@unique
class Weekday(Enum):
    Sun = 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

訪問這些枚舉類型可以有若幹種方法：

>>> day1 = Weekday.Mon
>>> print(day1)
Weekday.Mon
>>>
 
 print(Weekday.Tue)
Weekday.Tue
>>> print(Weekday['Tue'].name)
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

Python枚舉類