本篇主要介绍 Python 中枚举类的用法, 更多内容请参考: Python 学习指南
当我们需要定义常量时, 一个办法就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
好处就是简单, 确定是类型是 int, 并且仍然是变量.
更好的办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 来来实现这个功能:
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 类型的枚举值, 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 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:
@unique
class Weekday(Enum):
Sun = 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'].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
来源: http://www.bubuko.com/infodetail-2478564.html