http://www.cnblogs.com/codingmylife/archive/2013/05/31/3110656.html
python 3.4+
from enum import Enum
message_type=Enum('message_type','un_read readed deleted')
print(message_type.un_read.value)
print(message_type.readed.value)
print(message_type.deleted.value)
print(dir(message_type.readed))
# 或者
class MessageType(Enum):
un_read = 1
readed = 2
deleted = 3
print(MessageType.deleted.value)
# 1
# 2
# 3
# ['__class__', '__doc__', '__module__', 'name', 'name', 'value', 'value']
# [Finished in 0.2s]