（python）创建一个可以比较的自定义类

示例：

对于论坛中的帖子，需要根据帖子的点赞数，浏览数和评论数进行排序。三个排序标准的优先级顺序为：点赞数>浏览数>评论数。

也就是说，先按点赞数排序，如果点赞数相等，其次才按浏览数，最后才是评论数。

此外，如果要实现再set里面增加时，要保证不增加重复的，需要增加__hash__()

实现：

class Post:
    """"""
    def __init__(self,postname='',zan_num=0,view_num=0,reply_num=0):
        self.postname = postname
        self.zan_num = zan_num
        self.view_num - view_num
        self.reply_num = reply_num

    def __cmp__(self,other):
        if self.__eq__(other):
            return 0
        elif self.__lt__(other):
            return -1
        elif self.__gt__(other):
            return 1

    def __eq__(self,other):
        if not isinstance(other,Post):
            raise TypeError,"can't cmp other type to Post!"
        if self.zan_num == other.zan_num and self.view_num == other.view_num and self.reply_num == reply_num:
            return True
        else:
            return False
    def __lt__(self,other):
        if not isinstance(other,Post):
            raise TypeError,"can't cmp other type to Post!"
        if self.zan_num < other.zan_num:
            return True
        elif self.zan_num == other.zan_num and self.view_num < other.view_num:
            return True
        elif self.zan_num == other.zan_num and self.view_num = other.view_num and self.reply_num < other.reply_num:
            return True
        else:
            return False
    def __gt__(self,other):
        if not isinstance(other,Post):
            raise TypeError,"can't cmp other type to Post!"
        if self.zan_num > other.zan_num:
            return True
        elif self.zan_num == other.zan_num and self.view_num > other.view_num:
            return True
        elif self.zan_num == other.zan_num and self.view_num = other.view_num and self.reply_num > other.reply_num:
            return True
        else:
            return False

    def __hash__(self):
        return hash(self.postname)

#比较
post1 = Post('abc',42,12,33)
post2 = Post('acc',52,65,34)
post3 = Post('adc',42,13,53)
post4 = Post('aec',33,12,22)
print 'post2>post1':post1>post2
#排序：
post_lst = [post1,post2,post3,post4]
post_lst.sort(key=lambda obj:obj, reverse=True)